Devlin R H, Holm D G, Morin K R, Honda B M
Department of Biological Sciences, Simon Fraser University, Burnaby, B.C., Canada.
Genome. 1990 Jun;33(3):405-15. doi: 10.1139/g90-062.
Although little is known about the molecular organization of most genes within heterochromatin, the unusual properties of these chromosomal regions suggest that genes therein may be organized and expressed very differently from those in euchromatin. We report here the cloning, by P transposon tagging, of sequences associated with the expression of the light locus, an essential gene found in the heterochromatin of chromosome 2 of Drosophila melanogaster. We conclude that this DNA is either a segment of the light locus, or a closely linked, heterochromatic sequence affecting its expression. While other functional DNA sequences previously described in heterochromatin have been repetitive, light gene function may be associated, at least in part, with single-copy DNA. This conclusion is based upon analysis of DNA from mutations and reversions induced by P transposable elements. The cloned region is unusual in that this single-copy DNA is embedded within middle-repetitive sequences. The in situ hybridization experiments also show that, unlike most other sequences in heterochromatin, this light-associated DNA evidently replicates in polytene chromosomes, but its diffuse hybridization signal may suggest an unusual chromosomal organization.
尽管对于异染色质中大多数基因的分子组织了解甚少，但这些染色体区域的异常特性表明其中的基因可能与常染色质中的基因在组织和表达上有很大不同。我们在此报告通过P转座子标签法克隆与“亮区”基因表达相关的序列，“亮区”基因是在黑腹果蝇2号染色体异染色质中发现的一个必需基因。我们得出结论，该DNA要么是“亮区”基因的一个片段，要么是一个紧密连锁的、影响其表达的异染色质序列。虽然之前在异染色质中描述的其他功能性DNA序列都是重复序列，但“亮区”基因的功能可能至少部分与单拷贝DNA相关。这一结论是基于对P转座元件诱导的突变和回复突变的DNA分析得出的。克隆区域的不同寻常之处在于，这种单拷贝DNA嵌入在中等重复序列中。原位杂交实验还表明，与异染色质中的大多数其他序列不同，这种与“亮区”相关的DNA显然在多线染色体中复制，但其弥散的杂交信号可能表明其染色体组织异常。
