A mouse histone H4 gene carried by an SV40 vector is accurately expressed in infected monkey cells

Cell cycle regulation of a mouse histone H4 gene requires the H4 promoter

The mouse histone H4 gene, when stably transformed into L cells on the PSV2gpt shuttle vector, is cell cycle regulated in parallel with the endogenous H4 genes. This was determined in exponentially growing pools of transformants fractionated into cell cycle-specific stages by centrifugal elutriation, a method for purifying cells at each stage of the cell cycle without the use of treatments that arrest growth. Linker additions in the 5' noncoding region of the H4 RNA or in the coding region of the gene did not affect the cell cycle-regulated expression of the modified H4 gene even though the overall level of expression was altered. However, replacing the H4 promoter with the human alpha-2 globin promoter, so that the histone transcript produced by the chimeric gene remains essentially unchanged, resulted in the constitutive expression of H4 mRNA during all phases of the cell cycle with no net increase in H4 mRNA levels during the G1-to-S transition. From these results we conclude that all the information necessary for the cell cycle-regulated expression of the H4 gene is contained in the 5.2-kilobase subclone used in these studies with 228 nucleotides of 5'-flanking DNA and that the increase in H4 mRNA during the G1-to-S transition in the cell cycle is mediated by the H4 promoter and not by the increased stability of the H4 RNA.

Cell cycle regulation of a mouse histone H4 gene requires the H4 promoter

The mouse histone H4 gene, when stably transformed into L cells on the PSV2gpt shuttle vector, is cell cycle regulated in parallel with the endogenous H4 genes. This was determined in exponentially growing pools of transformants fractionated into cell cycle-specific stages by centrifugal elutriation, a method for purifying cells at each stage of the cell cycle without the use of treatments that arrest growth. Linker additions in the 5' noncoding region of the H4 RNA or in the coding region of the gene did not affect the cell cycle-regulated expression of the modified H4 gene even though the overall level of expression was altered. However, replacing the H4 promoter with the human alpha-2 globin promoter, so that the histone transcript produced by the chimeric gene remains essentially unchanged, resulted in the constitutive expression of H4 mRNA during all phases of the cell cycle with no net increase in H4 mRNA levels during the G1-to-S transition. From these results we conclude that all the information necessary for the cell cycle-regulated expression of the H4 gene is contained in the 5.2-kilobase subclone used in these studies with 228 nucleotides of 5'-flanking DNA and that the increase in H4 mRNA during the G1-to-S transition in the cell cycle is mediated by the H4 promoter and not by the increased stability of the H4 RNA.

Regulated expression of mammalian histone H4 genes in vivo requires a trans-acting transcription factor

Mouse L cells containing integrated copies of a human histone H4 gene have been obtained by cotransfection with the herpesvirus thymidine kinase gene. Nuclease S1 assays of RNA from several independent cell lines show that the expression of the introduced H4 gene is regulated during the cell cycle. One of these cell lines (line 6-8) contains more than 60 human H4 gene copies per haploid genome and does not express the endogenous mouse histone H4 mRNA. In contrast, the expression of the mouse H2a and H3 mRNAs in this cell line is not perturbed. In cell revertants that have lost the majority of the human H4 gene copies, the expression of the mouse H4 mRNA is restored, demonstrating that the mouse genes remain functional although not expressed. The rate of transcription of the histone H4 genes in clone 6-8 is at least 10-fold greater than that of the parental cell line and it is regulated during traversal of the cell cycle. These results show that the expression of mammalian histone H4 genes involves both a trans-acting transcriptional regulatory factor and an H4-specific activity. We propose that cell cycle regulation of histone gene expression may be effected through subtype-specific transcriptional regulatory proteins.