An amino-terminal tetrapeptide specifies cotranslational degradation of beta-tubulin but not alpha-tubulin mRNAs.
The steady-state level of alpha- and beta-tubulin synthesis is autoregulated by a posttranscriptional mechanism that selectively alters alpha- and beta-tubulin mRNA levels in response to changes in the unassembled tubulin subunit concentration. For beta-tubulin mRNAs, previous efforts have shown that this is the result of a selective mRNA degradation mechanism which involves cotranslational recognition of the nascent amino-terminal beta-tubulin tetrapeptide as it emerges from the ribosome. Site-directed mutagenesis is now used to determine that the minimal sequence requirement for conferring the full range of beta-tubulin autoregulation is the amino-terminal tetrapeptide MR(E/D)I. Although tubulin-dependent changes in alpha-tubulin mRNA levels are shown to result from changes in cytoplasmic mRNA stability, transfection of wild-type and mutated alpha-tubulin genes reveals that alpha- and beta-tubulin mRNA degradation is not mediated through a common pathway. Not only does the amino-terminal alpha-tubulin tetrapeptide MREC fail to confer regulated mRNA degradation, neither wild-type alpha-tubulin transgenes nor an alpha-tubulin gene mutated to encode an amino-terminal MREI yields mRNAs that are autoregulated. Further, although slowing ribosome transit accelerates the autoregulated degradation of endogenous alpha- and beta-tubulin mRNAs, degradation of alpha-tubulin transgene mRNAs is not enhanced, and in one case, the mRNA is actually stabilized. We conclude that, despite similarities, alpha- and beta-tubulin mRNA destabilization pathways utilize divergent determinants to link RNA instability to tubulin subunit concentrations.
Bachurski
C J
CJ
Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
Theodorakis
N G
NG
Coulson
R M
RM
Cleveland
D W
DW
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D006224:Cricetinae; D005786:Gene Expression Regulation; D006801:Humans; D019868:Kanamycin Kinase; D007700:Kinetics; D007739:L Cells; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000096:biosynthesis / Q000378:metabolism; D011132:Polyribosomes / Q000378:metabolism; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D014162:Transfection; D014404:Tubulin / Q000096:biosynthesis*
D012333:RNA, Messenger; D011994:Recombinant Proteins; D014404:Tubulin; D017853:Phosphotransferases (Alcohol Group Acceptor); D019868:Kanamycin Kinase