Accelerated mRNA decay in conditional mutants of yeast mRNA capping enzyme.
Current models of mRNA decay in yeast posit that 3' deadenylation precedes enzymatic removal of the 5' cap, which then exposes the naked end to 5' exonuclease action. Here, we analyzed gene expression in Saccharomyces cerevisiae cells bearing conditional mutations of Ceg1 (capping enzyme), a 52 kDa protein that transfers GMP from GTP to the 5' end of mRNA to form the GpppN cap structure. Shift of ceg1 mutants to restrictive temperature elicited a rapid decline in the rate of protein synthesis, which correlated with a sharp reduction in the steady-state levels of multiple individual mRNAs. ceg1 mutations prevented the accumulation of SSA1 and SSA4 mRNAs that were newly synthesized at the restrictive temperature. Uncapped poly(A)+ SSA4 mRNA accumulated in cells lacking the 5' exoribonuclease Xrn1. These findings provide genetic evidence for the long-held idea that the cap guanylate is critical for mRNA stability. The deadenylation-decapping-degradation pathway appears to be short-circuited when Ceg1 is inactivated.
Schwer
B
B
Microbiology Department, Cornell University Medical College, New York and Molecular Biology Program, Sloan-Kettering Institute, New York, NY 10021, USA.
Mao
X
X
Shuman
S
S
D005095:Exoribonucleases / Q000235:genetics; D005656:Fungal Proteins / Q000096:biosynthesis; D017353:Gene Deletion; D006360:Heat-Shock Proteins / Q000096:biosynthesis / Q000235:genetics; D018869:Heat-Shock Response; D009154:Mutation; D009713:Nucleotidyltransferases / Q000235:genetics*; D011500:Protein Synthesis Inhibitors; D012315:RNA Caps / Q000096:biosynthesis*; D012326:RNA Splicing; D012331:RNA, Fungal / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D012342:RNA, Small Nuclear / Q000032:analysis; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D000098556:mRNA Guanylyltransferases
D005656:Fungal Proteins; D006360:Heat-Shock Proteins; D011500:Protein Synthesis Inhibitors; D012315:RNA Caps; D012331:RNA, Fungal; D012333:RNA, Messenger; D012342:RNA, Small Nuclear; D029701:Saccharomyces cerevisiae Proteins; D009713:Nucleotidyltransferases; D000098556:mRNA Guanylyltransferases; D005095:Exoribonucleases; C068398:XRN1 protein, S cerevisiae