Comparison of exon 5 sequences from 35 class I genes of the BALB/c mouse
DNA sequences of the fifth exon, which encodes the transmembrane domain, were determined for the BALB/c mouse class I MHC genes and used to study the relationships between them. Based on nucleotide sequence similarity, the exon 5 sequences can be divided into seven groups. Although most members within each group are at least 80% similar to each other, comparison between groups reveals that the groups share little similarity. However, in spite of the extensive variation of the fifth exon sequences, analysis of their predicted amino acid translations reveals that only four class I gene fifth exons have frameshifts or stop codons that terminate their translation and prevent them from encoding a domain that is both hydrophobic and long enough to span a lipid bilayer. Exactly 27 of the remaining fifth exons could encode a domain that is similar to those of the transplantation antigens in that it consists of a proline-rich connecting peptide, a transmembrane segment, and a cytoplasmic portion with membrane-anchoring basic residues. The conservation of this motif in the majority of the fifth exon translations in spite of extensive variation suggests that selective pressure exists for these exons to maintain their ability to encode a functional transmembrane domain, raising the possibility that many of the nonclassical class I genes encode functionally important products.
Additional Information© 1989 Rockefeller University Press. After the Initial Publication Period, RUP will grant to the public the non-exclusive right to copy, distribute, or display the Article under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 International license, as described at https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode, or updates thereof. Received for publication 19 June 1989 and in revised form 22 August 1989. This work was supported by National Institute of Health Grant AI-17565. S. W. Hunt is a Special Fellow of the Leukemia Society of America. D. Nickerson was a visiting associate from the University of South Florida, Tampa, FL. We thank Drs. I. Stroynowski, M. Zuniga, K. Fischer Lindahl, and J. Kobori for critically reviewing this manuscript; Dr. J. Howard for critical insights on exon 5 evolution and sharing unpublished rat exon 5 sequence data; and Mrs. C. Blagg for expert secretarial assistance.
Published - BROjem89.pdf