Actin mRNAs in HeLa cells. Stabilization after adenovirus infection

We have carried out a comparative analysis of the expression of the actin genes in HeLa and adenovirus-infected HeLa cells. The rate of actin gene transcription was examined in these cells by pulse-labeling of the newly synthesized RNA and/or by in vitro transcription in nuclei isolated from uninfected or infected HeLa cells. In addition, accumulation of actin-specific heterogeneous nuclear RNA, and rate of appearance of the actin mRNAs in the cytoplasm were examined by dot and Northern blot analysis. The rate of actin gene transcription remained constant after infection of HeLa cells with adenovirus serotype 2, while the level of the actin precursor in the nuclei was slightly reduced. In the infected cells, newly synthesized actin mRNA enters the cytoplasm at a very reduced rate. The deficiency of transport does not affect the steady-state level of the messages in the cytoplasm. The half-life of cytoplasmic actin mRNAs was analyzed by traditional pulse-chase experiments and by a novel procedure using 5-6-diCl-1-beta-d-ribofuranosylbenzimidazole, which does not rely on labeled RNA. Both procedures gave identical results. Uninfected HeLa cells have actin mRNAs with relatively short half-lives, from less than six to 12 hours. In contrast, the half-lives of the actin-specific mRNAs, in the cytoplasm of adenovirus-infected cells, is greater than 14 to 24 hours. These observations suggest that, although the rate of transport of actin mRNAs to the cytoplasm is reduced upon infection with adenovirus, increased half-lives result in accumulation of actin mRNAs to normal levels in the cytoplasm.