Three distinct transforming genes present in human-tumor cell lines are all related to the viral oncogenes of Harvey and Kirsten murine sarcoma viruses, designated v-H-ras and v-Kras, respectively. The transforming gene of a bladder carcinoma cell line has been shown to be a human homolog to v-H-ras [Parada, L. F., Tabin, C.

The location of the translational termination codon for the transmembrane protein (TMP) varies in three infectious molecular clones of simian immunodeficiency virus from macaques (SIVmac). The SIV.aC251 and SIVmaC142 infectious clones have premature stop signals that differ in location by one codon; transfection of these DNAs into human HUT-78 cells yielded virus with a truncated TMP (28 to 30 kilodaltons [kDa]).

We induced AKR thymomas by injecting retrovirus MCF 247 that we had tagged with a fragment of phage X in its U3 region. About 10-20% of the 26 primary tumors studied showed both rearranged and germline c-myc bands in Southern blots. The rearranged c-myc genes were cloned from two of the tumors and studied by Southern analysis in two others. In all four cases, rearrangement was due to integration of MCF 247 proviruses about 2 kilobases (kb) 5' of the three cmyc exons and in the opposite transcriptional orientation. Thus, viral integrations were clustered within a 1-kb range in the tumors that revealed c-myc rearrangements. Three of the four proviruses appeared to be intact, whereas the fourth had an internal deletion of about 3 kb.

Information on the extent of genetic variability among non-human primate lentiviruses related to human immunodeficiency virus (HIV) is sorely lacking. Here we describe the isolation of two molecular clones from the simian immunodeficiency virus (SIV) and their use to derive restriction endonuclease maps of five SIV isolates from rhesus macaques and one from a cynomolgus macaque. Although similar, all six viral isolates are readily distinguishable; the single isolate from a cynomolgus macaque is the most different. The restriction endonuclease map of one macaque isolate (SIVMAC-251) is identical to that published by others for STLV-IIIAGM of African green monkeys and for HTLV-IV of humans. Nucleotide sequences from the envelope region of cloned SIVMAC-251 have more than 99% identify to previously published sequences for STLV-IIIAGM (refs 2, 4) and HTLV-IV (ref. 4). These results and other observations provide strong evidence that isolates previously referred to as STLV-IIIAGM and HTLV-IV by others are not authentic, but were derived from cell cultures infected with SIVMAC-251.

Conjugates of two unlike proteins can be prepared via the intermolecular disulfide interchange reaction, namely, protein A containing thiol groups reacts with protein B containing 4-dithiopyridyl groups to yield a conjugate with the release of 4-thiopyridone. Thiol groups can be introduced into proteins upon amidination with methyl 3-mercaptopropionimidate ester or 2-iminothiolane, and 4-dithiopyridyl groups can be introduced into proteins with these same reagents in the presence of 4,4'-dithiodipyridine. 2-Iminothiolane is stable on storage in contrast to the known lability of imidate esters; therefore 2-iminothiolane is a more convenient reagent for the modification of protein than are the imidate esters. All the reactions can be carried out easily under mild conditions in good yields. Conjugates of bovine plasma albumin with itself, ribonuclease, or a copolymer of D-glutamic acid and D-lysine and of sheep antibody and horseradish peroxidase were prepared with modified proteins containing an average of 1 to 5 thiol or dithiopyridyl groups per mol. These conjugates formed mainly dimers, trimers, and tetramers. The peroxidase labeled antibody retained more than 80% of its enzymatic and antigenic binding activities.