Molecular Biology Terms Starting With Y
Molecular Biology Glossary: Y
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Y RNA
/ WHY R-N-A / · Named for its Y-shaped secondary structure
Y RNA is a class of small non-coding RNA molecules, ranging from 70 to 100 nucleotides in length, that adopt a Y-shaped stem-loop structure and are required for the initiation of chromosomal DNA replication in eukaryotes.
Originally identified as autoantigens targeted by autoantibodies in patients with Systemic Lupus Erythematosus, Y RNAs are recognized by the Ro60 and La RNA-binding proteins that together form the Ro ribonucleoprotein particle. Depletion of Y RNAs from Xenopus laevis egg extracts blocks chromosomal DNA replication entirely, and adding purified Y RNA back to those extracts restores replication origin firing, establishing a direct requirement for these molecules. Humans express four Y RNA genes, designated hY1, hY3, hY4, and hY5, which are transcribed by RNA polymerase III and exported to the cytoplasm.
Beyond replication, Y RNAs contribute to RNA quality control by directing misfolded non-coding RNAs to degradation pathways.
Caenorhabditis elegans expresses only two Y RNA genes, yet both are required for embryonic DNA replication; worms in which both genes are silenced by RNA interference arrest development at the one-cell stage, demonstrating that Y RNA function is conserved across animals separated by hundreds of millions of years of evolution.
Building Blocks of Nucleic Acids →Short non-coding RNAs are all microRNAs. Y RNAs belong to a structurally and functionally distinct class that does not silence genes through complementary base pairing with mRNA targets.
In Xenopus laevis egg extract experiments, immunodepletion of Y RNAs reduces DNA replication efficiency to less than 10 percent of control levels. Replication origin firing is restored when synthetic Y RNA is added back at concentrations matching those found in intact eggs, approximately 50 nanomolar.