We study the biosynthesis of transfer RNA (tRNA) molecules, which serve as adaptors in transferring the genetic information from mRNA to protein. Specifically, we investigate transcription of human tRNA genes by RNA polymerase III (Pol III) and processing and splicing of newly transcribed precursor tRNAs.

Processing of precursor tRNA requires ribonuclease P (RNase P), an essential ribonucleoprotein enzyme. Biochemical purification analyses of nuclear RNase P from human cells have revealed that this large ribonucleoprotein complex has an RNA subunit, termed H1 RNA, and at least ten distinct protein subunits. We have characterized many of these protein subunits and reconstituted the endonucleolytic activity of RNase P in the processing of precursor tRNA in vitro by the use of H1 RNA and recombinant protein subunits. The roles of H1 RNA and its protein components in RNA-based catalysis and substrate recognition are being further investigated.

More recent discoveries from our laboratory reveal that a form of human RNase P is required for transcription of small noncoding RNA genes by Pol III. Pol III transcribes an expanding number of genes, including tRNA, 5S rRNA, SRP RNA, 7SK RNA and U6 snRNA genes. The noncoding RNA transcripts of these genes participate in fundamental biological processes, such as transcription, mRNA splicing, and translation. RNase P associates with initiation complexes of Pol III, known to be controlled by proto-oncogenes and tumor suppressor genes, and binds to chromatin of tRNA and 5S rRNA genes in a cell cycle-dependent manner. Ongoing research focuses on the elucidation of the molecular mechanisms by which RNase P exerts its role in distinct types of initiation complexes of Pol III and how transcription and processing of nascent precursor tRNAs are coordinated.

An additional area of research concerns the molecular designing and use of RNase P for inactivation of expression of human genes associated with aging and cancer. This research led us to the discovery that RNase P and Pol III respond to cessation of replication progression and DNA damage that cause mitotic catastrophe and cell death of cancer cells. Moreover, through collaborative study, we have shown that a form of human RNase P is involved in DNA repair of double-stranded breaks (DSBs) via the homology-directed repair pathway.