5' processing of tRNA precursors can Be modulated by the human La antigen phosphoprotein.
Eukaryotic precursor (pre)-tRNAs are processed at both ends prior to maturation. Pre-tRNAs and other nascent transcripts synthesized by RNA polymerase III are bound at their 3' ends at the sequence motif UUUOH [3' oligo(U)] by the La antigen, a conserved phosphoprotein whose role in RNA processing has been associated previously with 3'-end maturation only. We show that in addition to its role in tRNA 3'-end maturation, human La protein can also modulate 5' processing of pre-tRNAs. Both the La antigen's N-terminal RNA-binding domain and its C-terminal basic region are required for attenuation of pre-tRNA 5' processing. RNA binding and nuclease protection assays with a variety of pre-tRNA substrates and mutant La proteins indicate that 5' protection is a highly selective activity of La. This activity is dependent on 3' oligo(U) in the pre-tRNA for interaction with the N-terminal RNA binding domain of La and interaction of the C-terminal basic region of La with the 5' triphosphate end of nascent pre-tRNA. Phosphorylation of La is known to occur on serine 366, adjacent to the C-terminal basic region. We show that this modification interferes with the La antigen's ability to protect pre-tRNAiMet from 5' processing either by HeLa extract or purified RNase P but that it does not affect interaction with the 3' end of pre-tRNA. These findings provide the first evidence to indicate that tRNA 5'-end maturation may be regulated in eukaryotes. Implications of triphosphate recognition is discussed as is a role for La phosphoprotein in controlling transcriptional and posttranscriptional events in the biogenesis of polymerase III transcripts.
Fan
H
H
Laboratory of Molecular Growth Regulation, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-2753, USA.
Goodier
J L
JL
Chamberlain
J R
JR
Engelke
D R
DR
Maraia
R J
RJ
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D001324:Autoantigens / Q000378:metabolism*; D002474:Cell-Free System; D004722:Endoribonucleases / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D010766:Phosphorylation; D011072:Poly U / Q000378:metabolism; D012322:RNA Precursors / Q000378:metabolism*; D012329:RNA, Bacterial / Q000378:metabolism; D016337:RNA, Catalytic / Q000378:metabolism; D012358:RNA, Transfer, Met / Q000378:metabolism; D043262:Ribonuclease P; D012261:Ribonucleoproteins / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D000097585:SS-B Antigen
D000251:Adenosine Triphosphatases; D001324:Autoantigens; D004722:Endoribonucleases; D011072:Poly U; D012322:RNA Precursors; D012329:RNA, Bacterial; D016337:RNA, Catalytic; D012358:RNA, Transfer, Met; D043262:Ribonuclease P; D012261:Ribonucleoproteins; D014157:Transcription Factors; D000097585:SS-B Antigen; C045783:pre-tRNA(Met); C468368:RPP14 protein, human