Which is not part of the post-transcriptional modifications?*1 pointadding a 5' capadding a poly-A tailcutting out the exonscutting out the introns

To determine which option is not part of post-transcriptional modifications, let's review the concepts involved in RNA processing:

1. Adding a 5' cap: This modification involves adding a methylated guanine nucleotide to the 5' end of the nascent mRNA transcript, which is crucial for mRNA stability and export from the nucleus.

2. Adding a poly-A tail: This modification entails the addition of a long sequence of adenine nucleotides (polyadenylation) to the 3' end of the mRNA, which also contributes to mRNA stability and regulates translation.

3. Cutting out the exons: Exons are the coding sequences of RNA that are retained in the final mRNA. Cutting out exons would mean removing segments that code for proteins, which does not occur during post-transcriptional modification.

4. Cutting out the introns: Introns are non-coding sequences that are removed from the pre-mRNA during splicing, a key step in post-transcriptional modification.

Conclusion

Based on this analysis, the option "cutting out the exons" is not part of post-transcriptional modifications. Therefore, the correct answer is:

Cutting out the exons.