Duplication and deletion in the human immunoglobulin epsilon genes

The human IgE gene encodes a polypeptide chain that is involved in allergic reactions and in the immune response to parasitic disease in man. We have cloned three chromosomal regions corresponding to this sequence and find that two of them derive from curiously duplicated gene segments that also encode IgA constant-region genes. One of the IgE sequences corresponds to the active gene, and its structure defines a complete amino acid sequence of the human IgE constant region. The other cloned segment is a pseudogene from which the first two IgE coding domains have been deleted and replaced by a switch-like sequence that also occurs close to the normal IgE gene. The third IgE segment remains unlinked to the other heavy-chain genes. Evidently, the epsilon-alpha locus has been the site of several complicated genetic rearrangements during recent evolutionary time.     

Regulation of chlorophyll apoprotein expression and accumulation. Requirements for carotenoids and chlorophyll.

Chlorophyll apoprotein accumulation and expression were examined in mutants of Chlamydomonas reinhardtii blocked at specific steps of carotenoid or chlorophyll synthesis. In the absence of carotenoids: 1) apoproteins of the core and light-harvesting complexes of photosystem I (CCI and LHCI, respectively) and photosystem II (CCII and LHCII, respectively) do not accumulate; 2) mRNAs for the CCI, CCII, and LHCII apoproteins accumulate to normal levels; and 3) synthesis of the chlorophyll apoproteins is differentially affected, or in some cases, not affected. In the absence of chlorophylls: 1) the apoproteins fail to accumulate; 2) mRNA levels for CCI and CCII apoproteins are relatively unchanged; 3) levels of LHCII apoprotein mRNA, but not rates of LHCII mRNA synthesis, are reduced in a light-dependent chlorophyll-synthesis mutant (ya12); and 4) synthesis of chlorophyll apoproteins is differentially affected or not affected in the case of several chloroplast-encoded apoproteins. These results demonstrate a direct role for carotenoids as well as chlorophylls in the stabilization of certain chlorophyll apoproteins and, for others, possibly in their translation. The data also indicate a role for chlorophyll synthesis in the stability of LHCII mRNA.