Cl. Hsu et A. Stevens, YEAST-CELLS LACKING 5'-]3' EXORIBONUCLEASE-1 CONTAIN MESSENGER-RNA SPECIES THAT ARE POLY(A) DEFICIENT AND PARTIALLY LACK THE 5' CAP STRUCTURE, Molecular and cellular biology, 13(8), 1993, pp. 4826-4835
Analysis of the slowed turnover rates of several specific MRNA species
and the higher cellular levels of some of these mRNAs in Saccharomyce
s 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 othe
r hand, the length of mRNA poly(A) chains found after pulse-labeling o
f cells lacking the exoribonuclesse, the cellular rate of synthesis of
oligo(dT)-bound mRNA, and the initial rate of its deadenylation appea
red quite similar to the same measurements in wild-type yeast cells. E
xamination of the 5' cap structure status of the poly(A)-deficient mRN
As 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 pol
y(A) - mRNA fraction is low in cap structure content. Further analysis
of the 5' termini by measurements of the rate of 5' --> 3' exoribonuc
lease 1 hydrolysis of specific full-length mRNA species showed that ap
proximately 50% of the xrn1 poly(A)-deficient mRNA species lack the ca
p structure. Primer extension analysis of the 5' terminus of ribosomal
protein 51A (RP51A) mRNA showed that about 30% of the poly(A)-deficie
nt molecules of the xrn1 cells are slightly shorter at the 5' end. The
finding of some accumulation of poly(A)-deficient mRNA species partia
lly lacking the cap structure together with the reduction of the rate
of mRNA turnover in cells lacking the enzyme suggest a possible role f
or 5' --> 3' exoribonuclease 1 in the mRNA turnover process.