Question

Cleavage and polyadenylation of the 3' end of pre-mRNA is a posttranscriptional modification common to most protein-coding mRNA. It facilitates binding to ribosomes for translation, stabilizes the mRNA molecule, and prevents its degradation by exonucleases.

Using recombinant DNA techniques, any gene that has a promoter for RNA polymerase II can instead be connected to a promoter for RNA polymerase I. This hybrid gene is transcribed by RNA polymerase I, but the transcript does not undergo 3' cleavage and polyadenylation.

Explain why the hybrid gene mRNA transcript does not undergo 3' cleavage and polyadenylation.

Answer 1

The hybrid gene mRNA transcript does not undergo 3' cleavage and polyadenylation because it is transcribed by RNA polymerase I instead of RNA polymerase II.

Step-by-step explanation:

The hybrid gene mRNA transcript does not undergo 3' cleavage and polyadenylation because it is transcribed by RNA polymerase I instead of RNA polymerase II. Cleavage and polyadenylation of the 3' end of pre-mRNA is a posttranscriptional modification that occurs during processing of mRNA transcribed by RNA polymerase II.

RNA polymerase I terminates transcription by protein- or RNA hairpin-dependent methods, while RNA polymerase II transcribes for 1,000 or more nucleotides beyond the gene template and cleaves the excess during pre-mRNA processing. Therefore, when a gene with a promoter for RNA polymerase II is connected to a promoter for RNA polymerase I, the resulting hybrid gene is transcribed by RNA polymerase I, leading to a transcript that does not undergo 3' cleavage and polyadenylation.