The authors wish to correct a mistake which appeared in the abstract to the above paper concerning the number of transcripts produced by DHFR alleles. The correct abstract is printed below.The Chinese hamster cell line, DC-3F, is heterozygous at the DHFR locus, and each allele can be distinguished on the basis of a unique DNA pattern, protein isoelectric profile and In the abundancy of the OHFR and mRNAs it expresses. Although each allele produces transcripts 1000,1650 and 2150 nucleotides in length, the relative distribution of these RNAs differs for each; the 2150 nt mRNA represents the major (60-) species generated from one allele, while the 1000 nt mRNA is the major species generated from the other. The allele that predominantly expresses the 2150 nt transcript is preferentially overexpressed when DC-3F cells are subjected to selection in methotrexate. We have analyzed the 3′ ends of both DHFR alleles and have found that the three major mRNAs arise by readthrough of multiple potyadenylatlon signals. A four base deletion in one allele changes the consensus polyadenylatlon signal AAUAAA to AAUAAU, resulting in the utilization of a cryptic polyadenylatlon signal lying 21 bp upstream. Surprisingly, this mutation in the third polyadenylatlon signal appears to affect not only the utilization of this signal, but also the efficiency with which the first signal, located 1171 bp upstream from the third site is utilized.
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