Normal human c-fgr cDNA clones were constructed by using normal peripheral blood mononuclear cell mRNA as a template. Nucleotide sequence analysis of two such clones revealed a 1,587-base-pair-long open reading frame which predicted the primary amino acid sequence of the c-fgr translational product. Homology of this protein with the v-fgr translational product stretched from codons 128 to 516, where 32 differences among 388 codons were observed. Sequence similarity with human c-src, c-yes, and fyn translational products began at amino acid position 76 of the predicted c-fgr protein and extended nearly to its C-terminus. In contrast, the stretch of 75 amino acids at the N-terminus demonstrated a greatly reduced degree of relatedness to these same proteins. To verify the deduced amino acid sequence, antibodies were prepared against peptides representing amino-and carboxy-terminal regions of the predicted c-fgr translational product. Both antibodies specifically recognized a 55-kilodalton protein expressed in COS-1 cells transfected with a c-fgr cDNA expression plasmid. Moreover, the same protein was immunoprecipitated from an Epstein-Barr virus-infected Burkitt's lymphoma cell line which expressed c-fgr mRNA but not in its uninfected fgr mRNA-negative counterpart. These findings identified the 55-kilodalton protein as the product of the human fgr protooncogene.

Human papillomavirus type 16 (HPV16) early proteins E6 and E7 have been implicated in maintenance of the malignant phenotype in cervical cancer. Transforming growth factors beta one and two (TGFI3s 1 and 2), polypeptides that regulate cellular growth and differentiation, reversibly inhibited expression of the HPV16 E6 and E7 genes in several immortal genital epithelial cell lines. Loss of E6 and E7 protein expression followed a dramatic timeand dose-dependent decrease in E6 and E7 RNA levels and was accompanied by cessation of cell proliferation. TGF,s 1 and 2 inhibited HPV16 RNA expression at the transcriptional level; inhibition was dependent upon ongoing protein synthesis. TGFj3s 1 and 2 also induced a sixto sevenfold increase in TGFi 1 RNA. Cells became partially resistant to the inhibitory effects of TGF,3 1 on cell growth and HPV early gene expression after prolonged cultivation in vitro or after malignant transformation. Thus, TGF(1 may function as an autocrine regulator of HPV gene expression in infected genital epithelial cells.

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Abstract. The fgr protooncogene is a member of the src family of protein tyrosine kinases. Recent studies have shown that normal myelomonocytic cells and tissue macrophages are the major sites offgr mRNA expression. In the present study, we have identified the fgr protooncogene protein product in HL60 cells and have examined its expression as a function of HL60 cell maturation. Whether induced toward monocytic or granulocytic lineages, p55 c-~" accumulated in HL60 cells during maturation. In differentiated cells, the protein was active as a protein tyrosine kinase and was localized to peripheral cell membranes. Demonstration that a myristyl group was covalently bound to the protein probably accounted for its subcellular distribution. These findings establish developmental regulation of p55c-~ r in a lineage that represents its natural site of expression.N 'EARLY half of the retrovirus oncogenes described to date either encode protein tyrosine kinases or share structural homology with genes specifying such enzymes. Discoveries identifying a small number of these oncogenic tyrosine kinases as altered versions of growth factor receptors provided impetus for the idea that dysregulation of pathways normally controlled by growth factors-such as platelet-derived growth factor (10, 33), colony-stimulating factor 1 (28), and epidermal growth factor (ll)-can be important steps in the oncogenic process. It would appear, however, that not all oncogenic protein tyrosine kinases represent transmembrane growth factor receptors. Tyrosine kinases specified by the src protooncogene (31) as well as the closely related products of cellularfgr (c-fgr) ~ (15, 17) and yes (30) genes do not possess hydrophobic domains able to span the plasma membrane and therefore lack extracellular ligandbinding domains.Although the src family of oncogenic proteins exhibits known enzymatic and transforming activities (for a recent review see 16), functions for their normal cellular counterparts have been elusive. The ubiquitous expression of cellular src (c-src) has implied the importance of this protooneogene for a variety of cell types but has provided little information con-V. Notario's present address is

We have evaluated the regulation of expression of the poly(ADP-ribose) polymerase gene during cell growth and replication. In a synchronized population of HeLa cells or in serum-stimulated WI-38 cells, steady-state levels of the polymerase mRNA were highest at late S and S-G2 phases and negligible in early S phase. Transcription did not solely account for the significant increase in the mRNA levels observed in late S phase by Northern analysis. The stability of the mRNA was dependent upon the percent proliferating cells in the culture. Accordingly, polymerase mRNA from cells in early exponential phase was significantly more stable than from cells in stationary phase of asynchronous growth. To clarify these observations, we utilized a novel heterologous expression system that involved murine 3T3 cells transfected with a human poly(ADP-ribose) polymerase cDNA under the control of a non-cell cycle-specific promoter. Cells were synchronized, and a comparison was made of the endogenous (murine) and exogenous (human) polymerase mRNA levels. Both the endogenous and the exogenous mRNA were specifically stabilized by the same mechanisms and only during late S phase; therefore, we concluded that mRNA pools for the polymerase are regulated at the post-transcriptional level. The heterologous expression system confirmed that the post-transcriptional regulation system in the mouse cells can recognize and faithfully regulate the human cDNA in response to the murine cell cycle signals. More importantly, the presence of extra copies (human) of the polymerase gene did not provide an increased amount of the total polymerase mRNA or protein and, in fact, the sum of the endogenous and exogenous mRNA in the transfected cells was approximately the same as the level of endogenous transcript in the control cells. This suggested that there might be a limit to the amount of polymerase protein accumulating in the cellular pool and thus levels of poly(ADP-ribose) polymerase may be autoregulated.