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I Giri

Publications and source records attributed to I Giri.

9 recordsLinked to original sources
PubMed1988

Structural and mutational analysis of E2 trans-activating proteins of papillomaviruses reveals three distinct functional domains.

The E2 proteins of papillomaviruses are able to transactivate the viral enhancers by interacting with the sequence ACCGN4CGGT found in all papillomavirus long control regions. Analysis of the alignment of the amino acid sequences of 10 E2 proteins reveals three distinct regions: two partially conserved domains at the N and C termini of the proteins and a region variable in size and sequence in the middle. A computer prediction of the secondary structure of the 10 sequences outlines interesting conserved features, including two long amphiphilic alpha helices at the N terminus. To analyse the respective roles of the different segments of these proteins, we constructed a set of in-frame deletion and insertion mutations in the E2 coding sequences of the bovine papillomavirus type 1 (BPV1) and cottontail rabbit papillomavirus (CRPV). The test of their capacity to trans-activate or repress different viral constructs shows that the C-terminal domain of the E2 proteins is involved exclusively in DNA binding whereas the N-terminal domain is probably required for interaction with other components of the transcriptional machinery. The inner variable domain may confer flexibility to the protein such that it will facilitate contacts of the two others with their respective targets.

Amino Acid Sequence↗
PubMed1988

Study of the E2 gene product of the cottontail rabbit papillomavirus reveals a common mechanism of transactivation among papillomaviruses.

The long control region (LCR) of the cottontail rabbit papillomavirus (CRPV) harbors a transcriptional promoter which can be transactivated, as reflected by cat gene expression, by cotransfection with plasmids which express the intact E2 open reading frame of CRPV, human papillomavirus type 18 (HPV18), and bovine papillomavirus type 1 (BPV1). The E2 protein of CRPV can also transactivate the LCRs of BPV1, HPV1, and HPV18 inserted in front of the cat gene in enhancer or promoter configuration. Competition experiments in vivo and binding studies with CRPV E2 protein synthesized in vitro suggest that the different E2 proteins transactivate transcription by a common mechanism involving binding to the same ACCG-CGGT target sequence. The C-terminal part of the protein is necessary for its DNA-binding function. Analysis of the transactivation data and of the LCR sequences of these four viruses suggests that the two cutaneous viruses (CRPV and BPV1) present a similar pattern of promoter regulation but that the activity of the promoters of genital human viruses is less dependent on E2 regulation and is at least partially regulated by cellular factors.

Animals↗
PubMed1985

Genomic structure of the cottontail rabbit (Shope) papillomavirus.

The nucleotide sequence of the cottontail rabbit papillomavirus (CRPV or Shope papillomavirus) genome has been determined. The overall organization of the genome is similar to that of the other three papillomaviruses already sequenced. The amino acid sequences of the putative viral proteins were compared to the available protein data banks. Of particular interest is the homology found between the COOH terminus of the E2 putative protein of the different papillomaviruses and the viral or cellular mos oncogene product. This analysis also reveals a specific feature of the rabbit virus that may be related to its natural oncogenic potential. One of its open reading frames (E6) shows significant homologies with the beta subunit of a family of ATP synthases from mitochondria, chloroplasts, and bacteria, including the conservation of amino acids residues involved in nucleotide binding. The viral noncoding region includes a highly A+T-rich segment and shows a complex array of repetitions and inverted repeats that may act as control elements for gene expression and genome replication.

Base Sequence↗
PubMed1984

Papillomavirus genomes: sequences and consequences.

The complete nucleotide sequences of four papillomavirus genomes recently determined (human papillomavirus types 1a and 6b, bovine papillomavirus type 1, and the Shope cottontail rabbit papillomavirus) shed light on the molecular genetics of these epitheliotropic viruses. The organization of the four genomes is very similar, and their comparative analysis suggests new hypotheses about the nature of the viral proteins, their involvement in virus structure, and their interaction with the host cell, the terminally differentiating keratinocyte. It also allows us to consider, at the molecular level, the problem of papillomaviruses' host range and evolutionary relationship.

Amino Acid Sequence↗
PubMed1983

Comparative studies of the expression of linked Escherichia coli gpt gene and BPV-1 DNAs in transfected cells.

A series of hybrid plasmids, containing two selective markers that can be expressed in mammalian cells have been constructed. These plasmids are derived from the pSV2gpt recombinant plasmid described by Mulligan and Berg (1980) and contain the entire BPV-1 DNA, or the HindIII-BamHI large transforming fragment (T69) or the early transforming region of polyoma virus DNA. DNA transfers into Fisher rat 3T3 cells were performed either by the calcium phosphate coprecipitation technique, or by protoplast fusion. For all plasmids, the frequency of formation of phenotypically transformed foci or of the expression of the gpt+ marker in selective medium have been scored comparatively. Both series of recombinant plasmids gave similar yield of gpt+ colonies, whereas BPV plasmids (both entire or T69 subgenome) transformed morphologically rat cells 8-50 times less frequently than their polyoma homologues. Although the pSV2gpt BPV-1 plasmids can replicate autonomously to high copy number in monkey COS cells, the rate of transcription of the BPV-1 genome in these cells is 10(2) to 10(3) times lower than that of gpt transcribed from the SV40 early promoter. This low rate of transcription may explain the low frequency of transformation by this viral DNA.

Animals↗
PubMed1982

Both early and late control sequences of SV40 and polyoma promote transcription of Escherichia coli gpt gene in transfected cells.

Eucaryotic expression vectors containing two selective markers, the herpes simplex 1 thymidine kinase gene (tk) and the Escherichia coli gpt gene (Eco gpt) coding for a xanthine-guanine phosphoribosyl-transferase ( XGPRT ) were constructed. These plasmids were used to transfect mouse Ltk- cells followed by selection of either tk+ or XGPRT + colonies. The transcription and maturation of the Eco gpt mRNA is dependent on the presence of a eucaryotic promoter sequence at its 5' end and on the presence of a viral intron and a poly(A) addition site at its 3' end ( Mulligan and Berg, 1980). Here, we report that both simian virus 40 (SV40) and polyoma early and late promoters permit the transcription of this gene integrated into the cellular genome. Polyoma DNA fragments lacking the TATA box, or both the TATA and CAAT boxes directing early transcription, efficiently promote Eco gpt expression. Furthermore, a fragment terminating approximately 300 nucleotides upstream of the initiation site of early RNA permits Eco gpt synthesis when the early strand is joined to the Eco gpt-coding strand. The SV40 early promoter is 2- to 3-fold more efficient than the controlling sequence of late transcription. These results strongly suggest that the switch from a predominance of early RNA to that of late RNA occurring after the onset of DNA replication is caused by the increase in the abundance of template and by the concomitant repression of early transcription by the T antigen. The presence of the tk gene in all the plasmids constructed permits the analysis of Eco gpt expression as a non-selected marker in tk+ clones selected for growth in HAT medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗