Kokoza V A, Raikhel A S
Department of Entomology, Michigan State University, East Lansing 48824-1115, USA.
J Biol Chem. 1997 Jan 10;272(2):1164-70. doi: 10.1074/jbc.272.2.1164.
Insect oocytes are extraordinarily specialized for receptor-mediated endocytosis of yolk protein precursors. The clathrin heavy chain (CHC) is the major structural protein of coated vesicles, the principal organelles of receptor-mediated endocytosis. To understand the role of clathrin in the development of the oocyte's powerful endocytotic machinery we determined the structure of the mosquito chc gene. The gene spans approximately 45 kilobases and its coding region is divided into seven exons, five of which encode the protein. Three distinct mature transcripts of this gene were identified in mosquito tissues. Two of them code isoforms of the CHC polypeptide differing in their NH2-terminal sequences, and are specifically expressed in female germ-line cells. The third transcript has a 3'-untranslated region about 1 kilobase longer than the other variants, and is found only in the somatic cells. Tissue-specific 5'-exon splicing and alternative polyadenylation of the primary transcript combine to give rise to these mRNAs. We identified two alternative promoters, distal and proximal, separated by approximately 10 kilobases involved in tissue-specific regulation of mosquito chc gene expression. Our data provide the first molecular evidence for complex structure and regulation of a chc gene, in this case occurring at both the transcriptional and post-transcriptional levels.
昆虫卵母细胞在受体介导的卵黄蛋白前体的内吞作用方面具有高度特异性。网格蛋白重链（CHC）是被膜小泡的主要结构蛋白，而被膜小泡是受体介导的内吞作用的主要细胞器。为了了解网格蛋白在卵母细胞强大的内吞机制发育中的作用，我们确定了蚊子chc基因的结构。该基因跨度约45千碱基，其编码区分为七个外显子，其中五个编码蛋白质。在蚊子组织中鉴定出该基因的三种不同的成熟转录本。其中两种编码CHC多肽的异构体，其NH2末端序列不同，并且在雌性生殖系细胞中特异性表达。第三种转录本的3'-非翻译区比其他变体长约1千碱基，并且仅在体细胞中发现。初级转录本的组织特异性5'-外显子剪接和可变聚腺苷酸化共同产生了这些mRNA。我们鉴定出两个可变启动子，远端和近端，相隔约10千碱基，参与蚊子chc基因表达的组织特异性调控。我们的数据为chc基因的复杂结构和调控提供了首个分子证据，在这种情况下，这种结构和调控发生在转录和转录后水平。
