Worm Breeder's Gazette 10(1): 57
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
We have cloned and characterized one member of the C. elegans H1 gene family, hhl-1, and our studies have shown it has several features atypical of a histone gene. hhl-1 was isolated from a Bristol clone bank by cross-hybridization to a sea urchin H1 gene (L. pictus). hhl-1 hybridized to four genomic fragments in a Southern blot of genomic DNA digested with various enzymes. We therefore estimate the H1 gene family contains four members. None of these genomic fragments hybridized to a clone containing core (H2A, H2B, H3, H4) histone genes, and an analysis of cosmids which overlap hhl-1 indicate there are no other histone genes nearby in the DNA surrounding hhl-1. These results support our original studies which indicated the core genes are clustered together, whereas the genes for H1 reside elsewhere in the genome. The nucleotide sequence of hhl-1 has also revealed properties which are unusual for a histone gene. hhl-1 has a poly(A) addition signal and Northern blots have confirmed the hhl-1 transcript fractionates with poly (A)+ RNA. The core histone transcripts of C. elegans (like most histone transcripts from other organisms) are not polyadenylated. The hhl-1 sequence is interrupted by a 100 bp segment bounded by C. elegans splice donor and acceptor sequences. The presence of an intron has been confirmed by S1 nuclease analysis of transcripts. Only the Tetrahymena H1 gene has previously been shown to have an intron. We have shown that C. elegans core genes share unique 5' and 3' consensus sequences that are putative sites of action of regulatory proteins. hhl-1 does not have these sequences. In addition to a 3' poly (A) addition signal, analysis of the upstream region of hhl-1 revealed a consensus sequence for the general transcription factor SP1. These observations suggest C. elegans H1 genes are regulated independently of the core genes. We plan to pursue the problem of histone gene regulation by studying DNA binding proteins and expression of transgenes. Recently, we have identified a possible tissue-specific histone transcript. In collaboration with Dr. Sam Ward (Carnegie Institution) , we have determined there is an H1 transcript which can only be detected in poly (A)+ RNA fractions from worms producing sperm (i.e., males and fem-3 homozygotes). It is absent from RNA from worms which do not produce sperm (i.e., old adult worms or fem-1 homozygotes). This sperm-specific transcript has a larger molecular weight than the hhl-1 mRNA found in all worms, and we are currently trying to clone the cDNA for this transcript.