Hotta Y, Stern H
Cell. 1981 Dec;27(2 Pt 1):309-19. doi: 10.1016/0092-8674(81)90414-1.
One of the factors regulating the accessibility of specific DNA sequences to endonuclease nicking during meiosis is a group of small nuclear RNA molecules, 125 nucleotides in length and transcribed by RNA polymerase III. These molecules (referred to as PsnRNA) are synthesized during meiotic prophase, when chromosomes are undergoing homologous pairing or are already paired. Accessibility to the meiotically active DNA sequences (P DNA) depends on an as-yet-undefined alteration in chromatin structure. PsnRNA is a critical factor in the alteration; it cannot be replaced by other forms of RNA. The specificity of the chromatin sites altered by PsnRNA appears to be a function of sequence complementarity between it and P DNA. Under in vivo conditions the effective action of PsnRNA depends on homologous chromosome pairing. Chromatin sites housing P-DNA sequences in nuclei isolated from cells lacking homologous pairing are not affected by meiotic endonuclease or DNAse II. Accessibility to these sites can be effected by incubation of the nuclei with PsnRNA, but only if the nuclei are from zygotene-pachytene cells. Analyses of pachytene nuclei preincubated with PsnRNA indicate that PsnRNA renders chromatin accessible to at least two endonucleases, meiotic endonuclease and DNAase II, and that it also limits such accessibility to regions housing the complementary P-DNA sequences.
在减数分裂过程中，调节特定DNA序列对内切核酸酶切口可及性的因素之一是一组小核RNA分子，其长度为125个核苷酸，由RNA聚合酶III转录。这些分子（称为PsnRNA）在减数分裂前期合成，此时染色体正在进行同源配对或已经配对。对减数分裂活跃的DNA序列（P DNA）的可及性取决于染色质结构中一种尚未明确的改变。PsnRNA是这种改变中的关键因素；它不能被其他形式的RNA所替代。由PsnRNA改变的染色质位点的特异性似乎是它与P DNA之间序列互补性的一种功能。在体内条件下，PsnRNA的有效作用取决于同源染色体配对。从缺乏同源配对的细胞中分离出的细胞核中，含有P - DNA序列的染色质位点不受减数分裂内切核酸酶或DNA酶II的影响。这些位点的可及性可以通过将细胞核与PsnRNA一起孵育来实现，但前提是细胞核来自偶线期 - 粗线期细胞。对用PsnRNA预孵育的粗线期细胞核的分析表明，PsnRNA使染色质对至少两种内切核酸酶（减数分裂内切核酸酶和DNA酶II）具有可及性，并且它还将这种可及性限制在含有互补P - DNA序列的区域。
