Sea urchin histone genes: the beginning and end of the message.

Abstract

The purpose of studies on the regulation of histone gene expression is to explain, for instance, how histone proteins arise in defined stoichiometric relationships in the chromatin, how transcription of histone genes is regulated in the cell cycle and how during the development of some species, histone variant genes are activated sequentially. The control of histone gene expression has m any interesting facets. One is struck by the major differences in balance and importance of the various regulatory mechanisms as they become apparent from investigations in m any laboratories. For example, in yeast, histone gene transcription is tightly coupled to the cell cycle, and the amounts of histone synthesized are determined largely by regulation of histone m RN A turnover (Hereford & Osley 1981). At the other extreme, there is the example of the maturing frog oöcyte where histone m RN A synthesis is uncoupled from DNA synthesis and yields pools of histone 1000-fold in excess of nuclear DNA mass (reviewed by Woodland 1980). Recent reports suggest that even the details of histone gene transcription may vary during the development of the species. The tandem histone gene clusters of sea urchin (G. Spinelli, unpublished results) and frog oocytes are transcribed polycistronically at least at some stages of their development (J. Gall, personal communication), whereas histone gene clusters of the cleaving sea urchin embryos appear to be transcribed monocistronically (Mauron et al. 1981). Finally, in the early embryo the partitioning of the m RN A between nucleus and cytoplasm may be also a regulative process (DeLeon al. 1983).