Cloning, Expression, and Mapping of Ribonucleases H of Human and Mouse Related to Bacterial RNase HI

We identified two human sequences and one mouse sequence in the database of expressed sequence tags that are highly homologous to the N-terminal sequence of eukaryotic RNases H1. The cDNAs for human RNASEH1 and mouse Rnaseh1 were obtained, their nucleotide sequences determined, and the proteins expressed in Escherichia coli and partially purified. Both proteins have RNase H activity in vitro and they bind to dsRNA and RNA-DNA hybrids through the N-terminal conserved motif present in eukaryotic RNases H1. The RNASEH1 gene is expressed in all human tissues at similar levels, indicating that RNase H1 may be a housekeeping protein. The human RNASEH1 and mouse Rnaseh1 cDNAs were used to isolate BAC genomic clones that were used as probes for fluorescence in situ hybridization. The human gene was localized to chromosome 17p11.2 and the mouse gene to a nonsyntenic region on chromosome 12A3. The chromosomal location and possible disease association of the human RNASEH1 gene are discussed.