Studies on the translational control of histone synthesis. I. Translation of histone messenger RNA by heterologous cell-free systems prepared from cells inactive in DNA synthesis

The translation of histone mRNA has been studied in a cell-free system prepared from mouse ascites cells treated with cytosine arabinoside to inhibit DNA synthesis. No difference in the efficiency of translation was observed with respect to an extract of control untreated cells. Moreover, a rabbit reticulocyte cell-free system can translate histone mRNA; thus, cells inactive in DNA synthesis can translate this mRNA. A search for an inhibitor of translation of histone mRNA was carried out by adding postribosomal supernatant from S-phase-synchronized HeLa cells treated with cytosine arabinoside, to the ascites cell-free system. No effect on the translation of histone mRNA was detected. Even when the cell-free system was reconstituted with ascites ribosomes and postribosomal supernatant from S-phase HeLa cells blocked in DNA synthesis, no effect on translation of histone mRNA was observed. These results suggest that the regulatory mechanism which couples histone to DNA synthesis does not involve synthesis of a factor specifically necessary for the translation of histone mRNA, nor the formation of a stable inhibitor. We cannot exclude, however, that an inhibitor of translation may be formed in amounts corresponding exactly to those of the histone mRNA present at the time of the block in DNA synthesis and that for this reason we have failed to find it in the postribosomal supernatant.