Intracellular events that follow the binding of growth factors to cellular receptors are virtually undefined at the molecular level. The identification and characterization of genes whose expression is cell cycle dependent is the first necessary step in the search for genes that actually control cell proliferation. I have isolated three cDNA clones derived from Syrian hamster sequences that hybridize to unique cytoplasmic RNAs induced which quiescent cells are stimulated to proliferate. Although the biological function of these G1-specific sequences is presently unknown, their role in cell cycle progression is supported by their similarities with several oncogenes implicated in cell growth. An intriguing relationship to human malignancy is suggested by elevated levels of these sequences in some human leukemias. The transcriptional or post-transcriptional processes responsible for the transient increase in cytoplasmic RNA of three specific G1-sequences will be determined. At different times following stimulation of serum-deprived cells, the rate of transcription, the levels of nuclear and cytoplasmic RNA, and the stability of mRNA will be determined. The level of expression of these three specific RNAs in a variety of differentiation arrested human leukemias will be correlated to a number of well defined characteristics specific for each type of leukemia to evaluate the role of these sequences in malignancy. To pursue studies in potential biochemical function, full-length cDNA clones corresponding to these three G1-specific sequences will be isolated, restriction mapped and sequenced. Sequence comparisons to a data base will reveal if any homologies exist to previously sequenced genes. Using the cDNA, Syrian hamster genomic clones corresponding to these three RNA sequences will be identified, isolated, and their transcriptional organization analyzed. Putative regulatory regions will be sequenced and comparisons will be performed to identify consensus regions for future studies. The completion of these studies sets the stage for future studies concerning the definition of the biological activities of these G1-specific sequences and their role in the control of normal and abnormal cell growth.
