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J E Smart

Publications and source records attributed to J E Smart.

At least 37 records · Page 2Linked to original sources
PubMed1981

Identification of the gene and mRNA for the adenovirus terminal protein precursor.

The precursor of the 55K adenovirus terminal protein is an 87K protein that is covalently linked to viral DNA. This protein is likely to be identical to the 80,000 dalton protein described by Challberg et al. (1980). The mRNA for the 87K terminal protein precursor, like that for the E2-72K DNA binding protein, is detectable at both early and late times of infection, and its production is sensitive to protein synthesis inhibition (Lewis and Mathews, 1980). The 87K protein, together with proteins of 105,000 and 75,000 daltons, are translated from leftward transcribed (1-strand) messenger RNAs that are complementary to the viral genome between positions 11.2 and 31.5. Additional hybridization to the region between coordinates 37.3 and 41 suggests that the RNA body is spliced to sequences mapping farther right in the genome. Electron microscopic heteroduplex analysis has revealed a family of 1-strand RNAs that probably encode these proteins. The RNA bodies extend from coordinated 30, 26 and 23 to 11.1, with leaders at 39, 68.5 and 75 map units, defining a new adenovirus early region. These RNAs and region E2 RNAs share the first leader and presumably the same promoter, and may be coordinately expressed. Virions of the protease-deficient adenovirus 2 mutant ts1 grown at the restrictive temperature contain only the 87K form; when grown at the permissive temperature they contain both the 87K and 55K forms, and an additional 62K form; wild-type virions contain only the 55K form. Peptide analysis shows all these proteins to be related. The DNA-protein complex containing the 87K form is active as a template for viral DNA replication in vitro. This data supports a model of adenovirus DNA replication in which the 87K terminal protein precursor is the primary translation product and primes DNA synthesis. The 87K precursor is processed curing virus maturation to the 55K terminal protein, possibly via a 62K intermediate form, by the virus-specified Ad2ts1 protease.

Adenoviruses, Human↗
PubMed1981

Characterization of sites for tyrosine phosphorylation in the transforming protein of Rous sarcoma virus (pp60v-src) and its normal cellular homologue (pp60c-src).

The transforming protein of Rous sarcoma virus (pp60v-src) and its normal cellular homologue (pp60c-src) appear to be protein kinases that phosphorylate tyrosine in a variety of protein substrates. In addition, pp60v-src and pp60-c-src are themselves phosphorylated on serine and tyrosine. It is likely that these phosphorylations serve to regulate the function(s) of pp60v-src and pp60c-src. We have therefore characterized the sites of tyrosine phosphorylation in the two proteins. Tyrosine phosphorylation of pp60v-src in infected cells occurs mainly (if not entirely) at residue 419 in the deduced amino acid sequence of the protein. Surrounding this residue is the sequence Leu-Ile-Glu-Asp-Asn-Glu-Tyr(P)-Thr-Ala-Arg. This peptide is distinguished by the fact that three out of the four amino acids that precede the phosphorylated tyrosine are acidic in nature. These results define what may prove to be a widely used site for tyrosine phosphorylation in the regulation of cellular function. The same site was phosphorylated when partially purified pp60v-src was used in a phosphotransfer reaction in vitro. The results with pp60c-src were more complex. The site of tyrosine phosphorylation in vitro appeared to be the same as that found in pp60v-src. By contrast, phosphorylation of pp60c-src in vivo apparently occurred at a different, and currently unidentified, tyrosine residue. It is therefore possible that pp60v-src and pp60c-src respond differently to regulatory influences in the intact cell.

Amino Acid Sequence↗
PubMed1978

Three species of polyoma virus tumor antigens share common peptides probably near the amino termini of the proteins.

Detergent extracts of polyoma virus-infected mouse cells contain three major proteins of approximately 100,000--108,000 (100K), 55,000 (55K) and 21,500 (22K) daltons, which react with sera obtained from rats carrying tumors induced by the virus. A comparison of the 35S-methionine-, 3H-leucine- and 3H-proline-labeled tryptic peptides of each of these proteins by cation-exchange chromatography followed by descending paper chromatography has shown that: at least five peptides are shared by all three T-reactive proteins; at least three peptides are shared by the 55K and 22K proteins, but not by the 100K protein; at least three peptides are found only in the 22K protein; at least six peptides are found only in the 55K protein; and at least sixteen peptides are found only in the 100K protein. The results are consistent with the hypothesis that the polypeptide chains of the 100K, 55K and 22K dalton tumor antigens of polyoma virus share a common virus-coded amino terminal region. The data also suggest that there is a portion of the polypeptide chains (probably immediately adjacent to the common amino terminal region of the molecules) that is shared by the 55K and 22K proteins, but not by the 100K protein (perhaps because this portion of the genetic information is spliced out of the messenger RNA coding for the 100K protein). The facts that all the peptides common to the 100K and 55K proteins are also found in the 22K protein and are thus assigned to the common amino terminal region of the molecules, and that there are several peptides unique to the 100K protein, as well as several peptides unique to the 55K protein, suggest that the presumed carboxy terminal portion of the polypeptide chain of the 100K protein is considerably, if not entirely, different from that of the 55K protein.

Amino Acid Sequence↗