title: Yeast cells lacking 5'-->3' exoribonuclease 1 contain mRNA species that are poly(A) deficient and partially lack the 5' cap structure.
abstract: Analysis of the slowed turnover rates of several specific mRNA species and the higher cellular levels of some of these mRNAs in Saccharomyces cerevisiae lacking 5'-->3' exoribonuclease 1 (xrn1 cells) has led to the finding that these yeast contain higher amounts of essentially full-length mRNAs that do not bind to oligo(dT)-cellulose. On the other hand, the length of mRNA poly(A) chains found after pulse-labeling of cells lacking the exoribonuclease, the cellular rate of synthesis of oligo(dT)-bound mRNA, and the initial rate of its deadenylation appeared quite similar to the same measurements in wild-type yeast cells. Examination of the 5' cap structure status of the poly(A)-deficient mRNAs by comparative analysis of the m7G content of poly(A)- and poly(A)+ RNA fractions of wild-type and xrn1 cells suggested that the xrn1 poly(A)- mRNA fraction is low in cap structure content. Further analysis of the 5' termini by measurements of the rate of 5'-->3' exoribonuclease 1 hydrolysis of specific full-length mRNA species showed that approximately 50% of the xrn1 poly(A)-deficient mRNA species lack the cap structure. Primer extension analysis of the 5' terminus of ribosomal protein 51A (RP51A) mRNA showed that about 30% of the poly(A)-deficient molecules of the xrn1 cells are slightly shorter at the 5' end. The finding of some accumulation of poly(A)-deficient mRNA species partially lacking the cap structure together with the reduction of the rate of mRNA turnover in cells lacking the enzyme suggest a possible role for 5'-->3' exoribonuclease 1 in the mRNA turnover process.
authors.affiliation: Biology Division, Oak Ridge National Laboratory, Tennessee 37831-8077.
authors.forename: C L
authors.initials: CL
authors.lastname: Hsu
authors.forename: A
authors.initials: A
authors.lastname: Stevens
mesh_terms: D001483:Base Sequence; D005095:Exoribonucleases / Q000378:metabolism*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D011061:Poly A / Q000378:metabolism*; D011132:Polyribosomes / Q000378:metabolism; D014176:Protein Biosynthesis; D012315:RNA Caps / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional; D012331:RNA, Fungal / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics*
chemical_list: D012315:RNA Caps; D012331:RNA, Fungal; D012333:RNA, Messenger; D011061:Poly A; D005095:Exoribonucleases