Enhancer-facilitated expression of prokaryotic and eukaryotic genes using human histone gene 5′ regulatory sequences

Abstract

We examined the structural and functional properties of a human H3 histone gene promoter. The complete nucleotide sequence of an H3 structural gene and 515 nucleotides of 5′ and 100 nucleotides of 3′ flanking sequences were determined. The upstream region of this cell cycle dependent H3 histone gene, designated pST519, contains consensus sequences typical of genes transcribed by RNA polymerase II. To address promoter function directly, we determined the capability of the 5′ flanking sequences to direct the transcription of two genes which are not functionally or structurally related. Fusion genes were constructed using the 5′ flanking sequences of this human H3 histone gene and either human β-globin or bacterial chloramphenicol acetyltransferase (CAT) coding sequences. Both of these fusion genes were expressed when transfected into HeLa cells. Under control of the pST519 histone gene promoter, a β-globin mRNA transcript was initiated at the appropriate H3 histone cap site, and this same H3 histone promoter supported expression of a functional CAT protein. The SV40 72 base pair (bp) enhancer, inserted upstream from the histone promoter in both fusion constructs, increased levels of β-globin and CAT expression. Expression of the pST519 H3 histone gene in COS cells in the absence of the SV40 72-bp enhancer confirmed that the sequences required for promoting transcription reside within the 750-bp 5′ flanking sequences and that the exogenous enhancer facilitates, but is not a prerequisite for, transcription. Enhancer-facilitated expression of a cell cycle dependent human H4 histone gene was also observed following transfection into mouse L cells and indicates that the regulatory sequences of human histone genes and transcription factors of mouse cells are compatible.