Further characterization of the c-mos transcript and its cell cycle specific expression in NIH3T3 cells

The mouse c-mos proto-oncogene is primarily expressed in germ cells. Our previous studies demonstrated c-mos RNA expression in mouse somatic cells, with the highest level present in the G(2) phase of the cell cycle (Tsui et al., 1993). We have identified the transcription start site of this G(2) specific c-mos transcript to be located about 1580 bp upstream from the open reading frame based on RT-PCR and RNase protection experiments. Upstream sequences containing this transcription start site directed highest expression of the luciferase reporter gene in M phase of the cell cycle. These results suggest that c-mos transcripts are produced in G, phase and that c-Mos protein albeit at extremely low levels would accumulate in M phase.