RNA recognition motif 2 in La autoantigen (La or SS-B or LARP3), La-related protein 7 (LARP7 or PIP7S) and similar proteins
This subfamily corresponds to the RRM2 of La and LARP7. La is a highly abundant nuclear phosphoprotein and well conserved in eukaryotes. It specifically binds the 3'-terminal UUU-OH motif of nascent RNA polymerase III transcripts and protects them from exonucleolytic degradation by 3' exonucleases. In addition, La can directly facilitate the translation and/or metabolism of many UUU-3' OH-lacking cellular and viral mRNAs, through binding internal RNA sequences within the untranslated regions of target mRNAs. LARP7 is an oligopyrimidine-binding protein that binds to the highly conserved 3'-terminal U-rich stretch (3' -UUU-OH) of 7SK RNA. It is a stable component of the 7SK small nuclear ribonucleoprotein (7SK snRNP), intimately associates with all the nuclear 7SK and is required for 7SK stability. LARP7 also acts as a negative transcriptional regulator of cellular and viral polymerase II genes, acting by means of the 7SK snRNP system. LARP7 plays an essential role in the inhibition of positive transcription elongation factor b (P-TEFb)-dependent transcription, which has been linked to the global control of cell growth and tumorigenesis. Both La and LARP7 contain an N-terminal La motif (LAM), followed by two RNA recognition motifs (RRMs), also termed RBDs (RNA binding domains) or RNPs (ribonucleoprotein domains).