Final answer:
mRNAs are generally unstable due to cis elements, with stability affected by RNA binding proteins and structural features such as the poly-A tail and cap. However, the question's notion that translation begins in the nucleus is incorrect; translation occurs in the cytoplasm.
Step-by-step explanation:
The majority of mRNAs are inherently unstable due to their cis elements, such as sequences found within the 5' and 3' untranslated regions (UTRs) which impact the stability of mRNA. The stability can be influenced by various factors including the binding of RNA binding proteins (RBPs). The RBPs can either increase or decrease mRNA stability, depending on which protein binds. For instance, a mutation in the 5'UTR that prevents protein binding to the region could affect mRNA stability and subsequent protein translation, possibly leading to an increase in stability if degradation signals are blocked.
Moreover, the addition of a poly-A tail and a cap structure at the mRNAs' ends are critical for efficient translation, suggesting that by default, mRNAs are meant to be stable enough for translation. Contrary to the question statement, mRNAs do not begin translation in the nucleus but rather in the cytoplasm after being processed and exported from the nucleus.