Modulation of transcription of sea urchin histone genes by a nuclear protein fraction: studies on the specificity of this activity using the amphibian oocyte microinjection assay

Abstract

The early and late histone genes from the sea urchin Strongylocentrotus purpuratus constitute a pair of developmentally regulated genes. The early genes are expressed throughout oogenesis and early development until the blastula stage while the late genes are expressed at low levels until blastula and at higher levels thereafter.

Cloned early and late histone H2b genes are transcribed upon injection into Xenopus laevis oocytes. Maxson et al. (1986), have shown that a protein fraction obtained from sea urchin gastrula chromatin stimulates the transcription of both early and late genes when it is injected into oocytes along with them.

I have used the technique of primer extension to characterize how several cloned genes are expressed in injected oocytes. The results show that chloramphenicol acetyltransferase (CAT) gene sequences are transcribed from multiple aberrant sites of the pSV2CAT plasmid as efficiently as from the correct start site. On the other hand, the sea urchin histone L1H2b gene and sea urchin Spec 1 gene are transcribed mainly from their correct start sites. Herpes simplex virus thymidine kinase (HSV tk) gene transcripton is also correctly initiated and the amount of transcripts produced is very high as compared to the other genes.

I have further studied the effect of the protein fraction from sea urchin gastrula chromatin on the expression of L1H2b gene injected into Xenopus oocytes, focusing on analyzing its specificity. The results show that this fraction contains a stimulatory activity for the transcription of L1H2b gene. The stimulation is reproducible and its magnitude is 10 fold on the average. I have also shown that the stimulation is specific for L1H2b and it does not affect either HSV tk or Spec 1 genes. The activity described may be attributed to a transcription factor that is involved in the developmental regulation of the histone genes in the sea urchin.