Jones C W, Kafatos F C
Cell. 1980 Dec;22(3):855-67. doi: 10.1016/0092-8674(80)90562-0.
We describe in detail two cloned chromosomal DNA segments from Antheraea polyphemus, each bearing multiple chorion genes. Two types of genes are found per segment, each in two or three copies: they belong to both major chorion multigene families (A and B), but are expressed during the same developmental period (middle choriongenesis in one segment, late in the other). A and B genes alternate and are paired, lie in divergent transcriptional orientation and are in very close proximity to each other (mRNA cap sites are separated by a 5' flanking sequence 264 or 325 bp long). Each AB pair is embedded within a large, tandemly repeating unit. Within that unit, the homologous 3' flanking sequences that separate gene pairs evolve rapidly and are frequently interrupted by long segments representing inserts (or deletions). These segments would decrease unequal crossing-over, facilitating rapid evolution of the chorion multigene families. A total of 10.4 kb of DNA has been sequenced, permitting detailed comparisons of genes, their introns, 5' flanking and immediately 3' flanking regions. Genes range over two orders of sequence similarity, from highly releated to very disparate (gene copies; members of the same multigene family; members of different families). Among their universal features are a common cap-site sequence, a single intron invariably located at the same position within the signal peptide-encoding region, and a Hogness box 21 to 23 nucleotides upstream from the cap site. Features of possible paired promoters occupying the short 5' flanking region are discussed. Genes evolve both by base substitutions and by segmental mutations, which are almost invariably deletions/insertions related to small, direct repeats.
我们详细描述了来自多音天蚕蛾的两个克隆染色体DNA片段,每个片段都带有多个绒毛膜基因。每个片段发现有两种类型的基因,每种基因有两个或三个拷贝:它们属于两个主要的绒毛膜多基因家族(A和B),但在同一发育时期表达(一个片段中为中期绒毛膜发生,另一个片段中为后期)。A基因和B基因交替排列并配对,处于相反的转录方向,彼此非常靠近(mRNA帽位点由264或325 bp长的5'侧翼序列隔开)。每对AB基因都嵌入在一个大的串联重复单元中。在该单元内,分隔基因对的同源3'侧翼序列快速进化,并经常被代表插入(或缺失)的长片段打断。这些片段会减少不等交换,促进绒毛膜多基因家族的快速进化。总共对10.4 kb的DNA进行了测序,从而能够对基因、其内含子、5'侧翼和紧邻的3'侧翼区域进行详细比较。基因的序列相似性范围跨越两个数量级,从高度相关到非常不同(基因拷贝;同一多基因家族的成员;不同家族的成员)。它们的共同特征包括一个共同的帽位点序列、一个始终位于信号肽编码区域内相同位置的单个内含子,以及一个位于帽位点上游21至23个核苷酸处的霍格内斯盒。讨论了占据短5'侧翼区域的可能配对启动子的特征。基因通过碱基替换和片段突变进化,片段突变几乎总是与小的直接重复相关的缺失/插入。