Translation attenuation via 3′ terminal codon usage in bovine csn1s2 is responsible for the difference in αs2‐ and β‐casein profile in milk

Abstract

αs2‐casein mRNA (csn1s2) is translated at 25% of the efficiency of β‐casein transcripts (csn2); however, the molecular mechanisms governing the difference are unknown. The main objective of this study was to identify molecular mechanisms that explain differential translational regulation between bovine β‐ and αs2‐ casein by assessing the role of putative translational regulatory factors in both cellular and cell‐free translation systems. Sequence analysis indicated that the two transcripts share similar primary and secondary structures around the coding region. Deleting and exchanging untranslated regions (UTRs) on the transcripts suggested that the 3′ UTR of csn2 and the 5′ UTR of csn1s2 exert stimulatory effects on translation yet their effectiveness depends on the upstream and downstream sequences with which they are associated. A stronger effect on translational efficiency was found in the coding region of csn1s2 which displays unfavourable codons at the 3′ terminus. Deletion of a 28‐codon fragment from the 3′ terminus of the csn1s2 coding region increased translation to a par with csn2. We conclude that the last 28 codons of csn1s2 is the main regulatory element that attenuates its expression and is responsible for the different translational expression of β‐ and αs2‐ casein mRNA.This research was supported by NSERC Canada.