Spoerel N A, Nguyen H T, Eickbush T H, Kafatos F C
Department of Biochemistry, University of Connecticut Health Center, Farmington 06032.
J Mol Biol. 1989 Sep 5;209(1):1-19. doi: 10.1016/0022-2836(89)90166-6.
Twenty-two pairs of chorion genes belonging to the A and B multigene families have been characterized and mapped within two segments of a 320 kb (1 kb = 10(3) bases or base-pairs) chromosomal walk in the domesticated silkmoth Bombyx mori. Eighteen of the gene pairs belong to two groups that are typified by the previously characterized A/B.L12 and A/B.L11 chorion gene pairs, and are defined by two respective types of short (approx. 280 base-pairs) bidirectional promoter sequences. In the chromosome, the L12-like and L11-like pairs are interspersed with each other and with the remaining four gene pairs, which have unrelated promoter sequences. We have sequenced the promoter regions and adjacent small exons of all L12-like and L11-like A and B genes in the walk. The L12-like promoters are highly conserved, whereas L11-like promoters are somewhat more variable. Reconsideration of previous data on RNA accumulation and disappearance during choriogenesis, in the light of the sequences, indicates that L12-like genes are developmentally early-middle, while L11-like genes correspond to two developmental subgroups, middle I and middle II. Sequence comparisons of all these promoters, as well as the previously characterized promoters of the developmentally late HcA and HcB genes, identify short elements of possible regulatory significance. The sequences, as well as extensive cross-hybridization analysis with short probes derived from the reference A/B.L12 gene pair, under carefully controlled conditions of stringency, indicate the occurrence of sequence transfers among A or B genes. These sequence transfers, which could result from gene conversions or unequal crossovers, are less abundant than in the HcA and HcB families, but do result in a patchwork of similarities and differences in the A and B genes. The transfers appear to be least frequent between the moderately divergent A genes that belong to different temporal classes, while the L12-like and L11-like B genes appear to be extensively homogenized in sequence.
在家蚕Bombyx mori中，属于A和B多基因家族的22对绒毛膜基因已被鉴定，并定位在一段320 kb（1 kb = 10³个碱基或碱基对）染色体步移的两个区段内。其中18对基因属于两组，它们以先前鉴定的A/B.L12和A/B.L11绒毛膜基因对为典型，由两种各自类型的短（约280个碱基对）双向启动子序列定义。在染色体上，L12样和L11样基因对相互穿插，也与其余四个具有不相关启动子序列的基因对穿插。我们已对染色体步移中所有L12样和L11样A和B基因的启动子区域及相邻的小外显子进行了测序。L12样启动子高度保守，而L11样启动子则有些多变。根据这些序列重新审视先前关于绒毛膜生成过程中RNA积累和消失的数据，表明L12样基因在发育上处于早期到中期，而L11样基因对应于两个发育亚组，即中期I和中期II。对所有这些启动子以及先前鉴定的发育后期HcA和HcB基因的启动子进行序列比较，确定了可能具有调控意义的短元件。这些序列，以及在严格控制的严谨条件下，用源自参考A/B.L12基因对的短探针进行的广泛交叉杂交分析，表明A或B基因之间发生了序列转移。这些序列转移可能是由基因转换或不等交换导致的，其发生频率低于HcA和HcB家族，但确实导致了A和B基因中相似性和差异的拼凑。在属于不同时间类别的中度分化的A基因之间，转移似乎最不频繁，而L12样和L11样B基因在序列上似乎广泛同质化。
