Research on small RNA gene expression was continued. RNA polymerase (pol) III is responsible for synthesizing transcripts such as tRNA and 55 rRNA which are required for protein synthesis, in addition to certain other small cytoplasmic transcripts such as Alu RNAs and Y RNAs. Investigation of mechanisms of pol III transcription and associated activities was continued. Alus are small retrotransposed elements endogenous to the human genome. About one million dispersed Alu elements constitute about 5% of the genetic material. Alu transposition, which depends on expression of Alu RNA, causes de novo genetic variability and insertional mutations in humans. Investigation of Alu RNA and Alu RNA binding proteins continued to yield insight into their complex regulation and propensity for retrotransposition. Y RNA-containing Ro RNPs are autoimmune antigens in humans and are targeted in autoimmune-mediated congenital complete heart block in infants. Summary of Major Findings: 1. SRP14-Alu RNA binding protein is associated with Alu transcripts in adenovirus-infected cells. This protein is overexpressed relative to other SRP subunits in primate cells. overexpression of this protein is associated with the presence of a trinucleotide repeat (TNR) in the coding region of the SRP14 genes of higher primates. The SRP14 TNR mutation in the SRP14 gene coincided with the evolutionary events that produced a very large deposition of Alu retrotransposed elements into the genomes of higher primates. 2. The human autoimmune antigen known as La is a transcription termination factor. La controls reinitiation of small RNA genes by also functioning as an (re)initiation cofactor for RNA polymerase III. This activity augments La's activity as a termination factor to recycle both pol III and stable transcription complexes. Efficient recycling is necessary for production of the high levels of small RNAs that accumulate in vivo such as tRNA and 5S rRNA. 3. The human Y RNA gene family was cloned and its position mapped. This gene family represents a unique locus of four distinct pol III transcribed genes and resides in the vicinity of the telomeric end of human chromosome 7q36. The linear order of the single copy hY RNA genes was determined in terms of centromere-to-telomere orientation. Pol III- responsive upstream control elements of hY RNA genes were characterized.
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