TRANSCRIPTION OF SEA-URCHIN PARACENTROTUS-LIVIDUS MESENCHYME BLASTULA HISTONE GENES AFTER HEAT SHOCK

Mesenchyme blastula sea-urchin embryos were heat-shocked at 31.degree. C and pulse-labeled with [3H]uridine. The nuclear RNA was fractionated on glyoxal/agarose gels and each RNA fraction hybridized with cloned early blastula histone DNA. After heat shock there is an accumulation of histone RNA molecules larger than the messenger and a decrease, with respect to the control, of 9-S histone RNA. Chasing of the heat shock RNA by incubation of the embryos with unlabeled uridine and cytidine restores the radioactivity (as well as the hybridization profiles) of control embryos. Furthermore saturation curves obtained by hybridizing histone DNA with labeled 9-S RNA, showed an absence of the histone messenger in the cytoplasm of heat-shocked embryos, whereas it was present in both control and chased embryo. The accumulated histone RNA in heat-shocked embryos is possibly the precursor of mature messengers.