Suresh and Gail are students in a lab working on mice with defects in the function of the HOX3A gene. In the special mouse line
they are working on, no sequence changes are present in the genomic DNA of HOX3A, but the gene is not expressed properly and a mutant phenotype results. In one mouse line, an mRNA is produced in normal amounts, but no HOX3A protein can be detected. Suresh thinks the absence of protein results from a change in RNA processing that prevents the inclusion of an exon in the final mRNA. Gail thinks the absence of protein results from some second gene that produces a protein that binds to the 3'UTR. Which of the two could be correct?
The pre-messenger RNA (pre-mRNA) transcript obtained after transcription of eukaryotic genes must undergo several processing events, including a process known as intron splicing, where introns (i.e., the non-coding sections of an RNA transcript) are removed and exons (coding regions) are joined to form a mature mRNA molecule. The three prime untranslated (3′-UTR) region of this mRNA can also bind to regulatory non-coding RNAs such as, for example, miRNAs which inhibit gene expression by inhibiting translation and/or by triggering its degradation. Moreover, the 3′-UTR region may also contain silencer sequences that bind to repressors in order to inhibit gene expression. On the other hand, translation refers to the process by which an ordered polypeptide chain (i.e., a protein) is synthesized by using the information contained in an mRNA molecule. In consequence, in the case under consideration, the mutation in the second gene could affect both RNA processing and the regulation of translation, thereby equally affecting HOX3A protein synthesis.
