Biomedical subjects

A M Koltunow

Publications and source records attributed to A M Koltunow.

6 recordsLinked to original sources

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

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

Promoter efficiency depends upon intragenic sequences.

Experiments concerning gene transcription in Xenopus oocytes have revealed that the efficiency of the HSV-TK promoter is dependent upon the nature of the attached gene sequences. Transcriptional efficiency of the TK promoter when attached to its own gene was 30-fold higher than that observed when the promoter was attached either to an avian keratin gene or to the chicken histone H2B gene. Furthermore, attachment of the keratin gene promoter to the TK gene resulted in a 20-fold increase in keratin promoter efficiency. It was found by subsequent experiments that the TK gene is able to exert a stimulatory influence upon attached promoter sequences. This cis effect was shown to be independent of orientation but dependent upon the distance between the DNA sequences involved.

Animals↗

PubMed1986

Intron sequences modulate feather keratin gene transcription in Xenopus oocytes.

We have shown that chicken feather keratin genes are transcribed at extremely low levels in Xenopus oocytes. Primer extension reactions using carefully selected primers have shown that none of the detectable transcripts are spliced. When the single intron, located in the 5' untranslated region, was removed from the gene, we observed a 5-fold increase in transcript initiation from the in vivo "cap" site. Significantly, this 5-fold increase was also observed when the feather keratin intron was replaced with a similar sized fragment from pBR322. We conclude that the efficiency of accurate transcriptional initiation of chicken feather keratin genes in the oocyte is affected by DNA sequences within the intron.

Animals↗