Primase p49 mRNA expression is serum stimulated but does not vary with the cell cycle.

Abstract

Expression of the small-subunit p49 mRNA of primase, the enzyme that synthesizes oligoribonucleotides for initiation of DNA replication, was examined in mouse cells stimulated to proliferate by serum and in growing cells. The level of p49 mRNA increased -10-fold after serum stimulation and preceded synthesis of DNA and histone H3 mRNA by several hours. Expression of p49 mRNA was not sensitive to inhibition by low concentrations of cycloheximide, which suggested that the increase in mRNA occurred before the restriction point control for cell cycle progression described for mammalian cells and was not under its control. p49 mRNA levels were not coupled to DNA synthesis, as observed for the replication-dependent histone genes, since hydroxyurea or aphidicolin had no effect on p49 mRNA levels when added before or during S phase. These inhibitors did have an effect, however, on the stability of p49 mRNA and increased-the half-life from 3.5 h to about 20 h, which suggested an interdependence of p49 mRNA degradation and DNA synthesis. When growing cells were examined after separation by centrifugal elutriation, little difference was detected for p49 mRNA levels in different phases of the cell cycle. This was also observed when elutriated Gl cells were allowed to continue growth and then were blocked in M phase with colcemid. Only a small decrease in p49 mRNA occurred, whereas H3 mRNA rapidly decreased, when cells entered G2/M. These results indicate that the level of primase p49 mRNA is not cell cycle regulated but is present constitutively in proliferating cells.

Cell cycle expression of two replicative DNA polymerases alpha and delta from Schizosaccharomyces pombe.

“…In actively cycling cells, however, the transcript, protein, and enzymatic activity of human DNA polymerase a are constitutively expressed throughout the cell cycle. Similar findings have been observed in several mammalian replication proteins (Sherley and Kelly, 1988;Wahl et al, 1988;Morris and Mathews, 1989;Tseng et al, 1989). It was also shown that in actively cycling cells the human DNA polymerase a protein is phosphorylated in a cell cycledependent manner .…”

“…In mammalian cells, most genes involved in DNA synthesis or metabolism are expressed constitutively during the cell cycle. In some cases, the proteins are modified posttranslationally in a cell cycle-dependent manner (Sherley and Kelly, 1988;Wahl et al, 1988;Morris and Mathews, 1989;Tseng et al, 1989;Nasheuer et al, 1991). In S. cerevisiae, the transcriptional expression of many DNA synthesis genes are coordinately induced at the Gl/S boundary.…”

Transcriptional and posttranscriptional regulation of the proliferating cell nuclear antigen gene.

“…The mRNA levels of the PCNA gene are growth regulated (1,15), as are those of other genes coding for proteins of the DNA-synthesizing machinery, such as the genes for TK (6,15,20,37), DNA polymerase alpha (41), RNA primase (40), and thymidylate synthase (16). In continuously dividing cells such as HeLa cells, the mRNA levels of some of these genes (those encoding TK [33], DNA polymerase alpha [41], RNA primase [40], and PCNA [23]) vary little throughout the cell cycle.…”

“…In continuously dividing cells such as HeLa cells, the mRNA levels of some of these genes (those encoding TK [33], DNA polymerase alpha [41], RNA primase [40], and PCNA [23]) vary little throughout the cell cycle. However, in quiescent fibroblasts or fibroblastlike cells in culture, the mRNA levels of these genes are very low or undetectable and increase sharply when serum-stimulated cells reach the G1/S boundary.…”

Post‐transcriptional regulation of the transferrin receptor and 4F2 antigen heavy chain mRNA during growth activation of spleen cells

“…In experiments where exponentially growing cells were separated by counterflow centrifugation it has become clear that both mRNA species are constitutively expressed throughout the cell cycle (Parmacek et al, 1989;Barker and Newburger, 1990). Thus, as described for several other growth-induced genes (Thompson et al, 1985;Wahl et a]., 1988;Tseng et al, 1989), expression of the 4F2 antigen and transferrin receptor increases upon activation of quiescent cells, but subsequently remains constant in continuously cycling cells. This rules out a regulatory control that is specific to the GI phase in each cycle.…”