Histone synthesis by cleavage arrested sea urchin eggs

A change in Hl histone synthesis occurs in blastulae, from Hlm to a faster moving Hlg in acrylamide gel electrophoresis. The experiments below indicate that this shift occurs in the absence of normal cleavage. Hybrid embryos containing paternal Hl histone markers along with homospermic embryos were studied. Both were labeled with L-[3H]lysine. Some cultures were kept at 11 degrees C to inhibit cleavage. It was found that Hlm and Hlg are synthesized sequentially in time by embryos grown at 20 degreet C as well as by those grown at 11 degrees C. The hybrid data establish that Hlm is translated at least in part from mRNA newly transcribed from paternal DNA. This observation also holds for cleavage inhibited hybrid embryos. Hlg is made by both hybrid and homospermic embryos during the later phases of development at both 11 and 20 degrees C. These results confirm and extend those of Seale et al. (1973), Ruderman et al. (1974) and Easton et al. (1974).