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M A Rezaian

Publications and source records attributed to M A Rezaian.

15 recordsLinked to original sources
PubMed1992

In vitro synthesis of an infectious viroid: analysis of the infectivity of monomeric linear CEV.

Infectious monomers of citrus exocortis viroid (CEV) were synthesized in vitro precisely to predetermined sequences in microgram quantities without resorting to cloning procedures. Amplification of CEV double-stranded cDNAs fused with a T7 RNA polymerase promoter was followed by transcription of the DNA resulting in the production of an infectious linear CEV monomer. This is the first demonstration of an infectious unit length viroid synthesized in vitro. Transcripts containing 3'-OH terminal groups were infectious, demonstrating that a 2',3'-cyclic phosphate terminus is not a prerequisite for viroid infectivity as previously suggested. Conversion of the 5'-triphosphate terminus to either 5'-monophosphate or 5'-OH had little effect on infectivity. The linear RNA could be circularized using T4 RNA ligase to produce an authentic CEV molecule. This procedure, which results in the production of biologically active RNA, would allow routine application of oligonucleotide-directed mutagenesis to the study of viroids and other circular RNAs. It would also enable the in vitro synthesis and mutagenesis of infectious viral RNAs containing a 5'-G residue.

Base Sequence↗
PubMed1992

Common identity of grapevine viroids from USA and Australia revealed by PCR analysis.

Pairs of viroid-specific oligonucleotide primers were selected and used in separate reverse transcription reactions coupled with the polymerase chain reaction to obtain DNA products of predetermined sizes characteristic of each viroid. The reaction conditions allowed efficient incorporation of small amounts of 32P-dATP which enabled rapid detection of the products in polyacrylamide gels. Using this method as well as probe hybridization, the presence of grapevine yellow speckle viroids 1 and 2 (previously known as GV1B) in grapevine samples from California was demonstrated, and it was established that the Australian grapevine viroid occurs in California. These comparisons provide the basis for uniform nomenclature of grapevine viroids found in different geographical regions.

Australia↗
PubMed1990

Australian grapevine viroid--evidence for extensive recombination between viroids.

Australian grapevine viroid (AGV, 369 residues) is a novel viroid with less than 50% sequence similarity with any known viroid. Nevertheless its entire sequence can be divided into regions, each with a high sequence similarity with segments from one of citrus exocortis, potato spindle tuber, apple scar skin, and grapevine yellow speckle viroids. AGV contains the entire central conserved region of the apple scar skin viroid group and is proposed as a member of this group. AGV appears to have originated from extensive RNA recombination involving other viroids. The vegetatively propagated grapevines which have been exposed to multiple viroid infections during their long history of cultivation may have allowed such recombination.

Base Sequence↗
PubMed1989

Grapevine viroid 1B, a new member of the apple scar skin viroid group contains the left terminal region of tomato planta macho viroid.

GV1B is one of five viroids that have recently been purified from grapevines. GV1B has now been sequenced and its 363 nucleotide residues can potentially form the typical rod-like structure of viroids with 67% of nucleotides base-paired. GV1B has highest sequence similarity with grapevine yellow speckle viroid (GYSV; 73%) and has a central sequence which is conserved in GYSV and apple scar skin viroid (ASSV) which have been reported to constitute the ASSV group. Therefore, we have placed GV1B into the ASSV group. GV1B contains a direct repeat sequence at the terminal portions of its T1 and T2 regions. GV1B also contains a sequence of 69 nucleotides in the terminal portion of its T1 region which is almost identical to the corresponding region in tomato planta macho viroid (TPMV). This provides further evidence of the importance of RNA recombination in viroid evolution.

Base Sequence↗
PubMed1989

Two related viroids cause grapevine yellow speckle disease independently.

We have confirmed that two closely related circular RNA molecules previously named grapevine yellow speckel viroid (GYSV) and grapevine viroid 1B (GV1B) are indeed viroids. Electron microscopy after spreading under non-denaturing conditions revealed that GYSV has a rod-like structure typical of viroids. Purified GYSV and GV1B replicated independently in inoculated grapevine seedlings and some of the infected plants developed yellow speckle symptoms indicating that both viroids can cause grapevine yellow speckle disease. Plus-sense RNA transcripts derived from a dimeric GYSV cDNA clone induced yellow speckle symptoms in a grapevine seedling confirming the role of GYSV in the yellow speckle disease. Two oligonucleotide probes were synthesized for the detection of the two related viroids. The probes which could detect each viroid individually were used to assess correlations between the occurrence of these viroids and the incidence of the disease.

Base Sequence↗
PubMed1989

A scheme for viroid classification.

A scheme for viroid classification is proposed based on the nature of the strictly conserved core sequence present in the central portion of the secondary structure of viroids. In this scheme, all of the known viroids can be classified as potato spindle tuber-type viroids consisting of two viroid groups and avocado sunblotch-type viroids containing one viroid group.

Base Sequence↗
PubMed1988

Grapevine yellow speckle viroid: structural features of a new viroid group.

A single stranded circular RNA was isolated from grapevines infected with yellow speckle disease. The RNA which we have called grapevine yellow speckle viroid (GYSV), contains 367 nucleotide residues and has the potential to form the rod-like secondary structure characteristic of viroids. GYSV has 37% sequence homology with the recently described apple scar skin viroid (ASSV; 330 residues) and has some sequence homology with the viroids in the potato spindle tuber viroid (PSTV) group. The sequence of GYSV has characteristics which fit the structural domains described for the PSTV group. However, GYSV lacks the PSTV central conserved sequence. Instead, there is a conserved sequence in the central region of GYSV and ASSV which has the potential to form a stem loop configuration and a stable palindromic structure as does the central conserved region of the PSTV group. These structural features suggest there is a different central conserved region for GYSV and ASSV. The results support the viroid nature of GYSV and its inclusion into a separate viroid group which we suggest should be represented by ASSV.

Base Sequence↗
PubMed1988

Isolation of three viroids and a circular RNA from grapevines.

Analysis of nucleic acids from grapevine tissues by two-dimensional gel electrophoresis demonstrated the presence of two bands of circular RNA. The smaller RNA contained about 300 nucleotide residues and was identified as hop stunt viroid by nucleotide sequencing. The larger RNA band was a mixture of species and contained similar amounts of two components, referred to as RNA 1a and RNA 1b, and in addition a trace amount of citrus exocortis viroid (CEV) which became detectable only after inoculation of the mixture to tomato. The identity of CEV was determined by probe hybridization and nucleotide sequencing. Both RNAs 1a and 1b are distinct from CEV and have estimated sizes larger than those of CEV and other viroids reported so far. RNA 1a preparations were infectious in cucumber and in tomato and the recovered viroid had unique properties. We have provisionally named this viroid Australian grapevine viroid. Evidence for the autonomous replication of RNA 1b was not obtained.

Base Sequence↗
PubMed1987

Nucleic acid extraction and virus detection in grapevine.

Three extraction media for the isolation of nucleic acids from grapevines, a tissue high in polyphenols and other materials that interfere with nucleic acid extraction, were compared. When phenol was present in the initial extraction media only a small yield of soluble RNA and no high molecular weight rRNA was obtained. In the absence of phenol in conventional salt and detergent-based extraction media, rRNAs were extracted, but a major proportion of the RNAs were broken down. Using Na-perchlorate, a chaotropic salt, in a rapid procedure, it was possible to extract both high and low molecular weight RNA efficiently. This procedure enabled the detection of viral RNA, which could not be detected following phenol extraction, at the picogram levels, by dot-blot hybridization.

Nucleic Acid Hybridization↗
PubMed1986

Anti-sense regions in satellite RNA of cucumber mosaic virus form stable complexes with the viral coat protein gene.

The interaction in vitro of the RNA of the Q-strain of cucumber mosaic virus (CMV) with its satellite RNA (sat-RNA) has been studied. In hybridisation reactions containing 30% formamide at 45 degrees, sat-RNA binds to CMV RNA 3 and 4 but not to CMV RNA 1 and 2 or RNA from tobacco mosaic virus and alfalfa mosaic virus. The viral coat protein gene present in RNA 3 and 4 contains the site of binding but this region does not contain complementary sequences of any significant length to the sat-RNA sequence. However, the optimum alignment of short complementary sequences present in these regions revealed a stable structure in which it is proposed that sat-RNA twists around the coat protein gene so that two separate blocks of nucleotides in sat-RNA base pair in opposite directions with two adjacent blocks in the coat protein gene to form a knot-like structure. The binding site is a region of 33 nucleotides within the coding region of the coat protein gene which base pairs with residues 98-113 and 134-152 of sat-RNA. The possibility of the binding region of sat-RNA functioning as an "anti-sense" sequence in regulation of the viral coat protein synthesis is discussed.

Base Sequence↗
PubMed1985

Nucleotide sequence of cucumber mosaic virus RNA. 1. Presence of a sequence complementary to part of the viral satellite RNA and homologies with other viral RNAs.

The nucleotide sequence of the 3389 residues of RNA 1 (Mr 1.15 X 10(6) of the Q strain of cucumber mosaic virus (CMV) was determined, completing the primary structure of the CMV genome (8617 nucleotides). CMV RNA 1 was sequenced by the dideoxy-chain-termination method using M13 clones carrying RNA 1 sequences as well as synthetic oligonucleotide primers on RNA 1 as a template. At the 5' end of the RNA there are 97 noncoding residues between the cap structure and the first AUG (98-100), which is the start of a single long open-reading frame. This reading frame encodes a translation product of 991 amino acid residues (Mr 110791) and stops 319 nucleotide residues from the 3' end of RNA 1. In addition to the conserved 3' region present in all CMV RNAs (307 residues in RNA 1), RNAs 1 and 2 have highly homologous 5' leader sequences, a 12-nucleotide segment of which is also conserved in the corresponding RNAs of brome mosaic virus (BMV). CMV satellite RNA can form stable base pairs with a region of CMV RNAs 1 and 2 including this 12-nucleotide sequence, implying a regulatory function. This conserved sequence is part of a hairpin structure in RNAs 1 and 2 of CMV and BMV and in CMV satellite RNA. The entire translation products of RNA 1 of CMV and BMV could be aligned with significant homology. Less prominent homologies were found with alfalfa mosaic virus RNA 1 translation product and with tobacco mosaic virus Mr-126000 protein.

Amino Acid Sequence↗
PubMedDate not supplied

Detection of virus-associated dsRNA from leafroll infected grapevines.

A simple procedure is described for reproducible detection of double stranded (ds) RNAs in leafroll infected grapevines. The procedure involves the extraction of tissues by a medium which preferentially yields dsRNA. The RNA is purified by CF11 cellulose chromatography and gel electrophoresis. The dsRNAs varied in size in different vines. In the cases tested they did not cross hybridize and occurred at higher concentrations in stem cortex tissues than in leaves. They were not detectable in healthy vines, could be passaged with the disease to healthy plants by graft inoculation and removed by virus elimination procedures. These observations indicated that the dsRNAs are of viral origin and that a number of viruses are associated with the grapevine leafroll disease.

Chromatography↗