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Comparative analysis of cosmid clones containing the human and feline c-sis genetic regions revealed the similar structural organization of these areas in the two species. The areas shared seven different genetic regions in and around the c-sis locus and of these was related to v-sis. Another region, 1.9 kbp in size and located about 8 kbp upstream of the v-sis homologous region in the human genome, also hybridized to the main c-sis transcriptional product of 3.5 kb. Comparison with a recently described c-sis cDNA clone (Collins et al., Nature 316, 748-750 (1985)) revealed that the 1.9 kbp DNA region contained a large 5' c-sis exon of at least 1050 bp. In this exon, the presumed initiation site of the predicted PDGF-2 containing precursor protein was located and appeared to be preceded by a large untranslated region. In the region immediately upstream of this exon, a TATA box and a consensus sequence for a potential Sp1 binding site were found at similar positions in both species. This region also exhibited promoter activity when tested in an assay in which coding sequences of bacterial chloramphenicol acetyltransferase (CAT; acetyl-CoA: chloramphenicol 3-O-acetyltransferase, EC 2.3.1.28) were placed under its control. The five other DNA regions were found upstream and downstream of the human c-sis transcription unit and also in an intron. Four of them contained repetitive sequences. Hybridization analysis of human and feline c-sis containing cosmid clones with a mixed synthetic nucleotide probe, which corresponded to sequences encoding amino acid residues 2-7 of chain 1 of platelet-derived growth factor (PDGF-1), suggested that the c-sis cosmid clones did not include PDGF-1-specific genetic sequences.

This communication describes the application of the 2‐(methylsulfonyl)ethyl group (Mse) as a base‐labile protecting group for the two hydroxyl functions in phosphoric acid monoesters. Due to its perfect stability towards acids, the Mse group can function as a stable protecting group in a phosphochloridate, providing a suitable phosphorylating agent. Some model phosphorylations are presented, and the reaction is applied to the synthesis of bis[2‐(methylsulfonyl)ethyl] tyrosine phosphate. Removal of the Mse functions is achieved effectively and extremely rapidly in alkaline media. The estimation of the minimum conditions necessary for the removal of one or both Mse functions from bis[2‐(methylsulfonyl)ethyl] p‐nitrophenyl phosphate and from a tyrosine derivative is described.

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