A point mutation changes the hexanucleotide sequence located 10 to 30 nucleotides upstream of a eukaryotic gene's 3' cleavage site. The most likely consequence for the resulting mature mRNA is:

• A Retention of the final intron due to failed spliceosome assembly
• B Loss of the 7-methylguanosine cap and failure of ribosome scanning
• C Use of an internal downstream AUG with an N-terminally truncated protein
• D Failure of cleavage and polyadenylation, producing a tail-less transcript that is rapidly degraded ✓

Explanation

The sequence AAUAAA, bound by cleavage and polyadenylation specificity factor (CPSF), directs endonucleolytic cleavage about 10 to 30 nucleotides downstream and subsequent addition of the poly-A tail by poly(A) polymerase. Mutation of AAUAAA abolishes cleavage, so the pre-mRNA is neither polyadenylated nor properly terminated; the unprotected transcript is rapidly degraded by 3' exonucleases. Cap formation and splicing occur at the 5' end and introns respectively and are unaffected by this 3' end signal.

Reference: Lewin's Genes, 13th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.