Mazan S, Mattei M G, Passage E, Bachellerie J P
Centre de Recherche de Biochimie et de Génétique Cellulaires, Centre National de la Recherche Scientifique (C.N.R.S.), Toulouse, France.
Cytogenet Cell Genet. 1991;56(1):18-22. doi: 10.1159/000133037.
U3 small nucleolar RNA, which is believed to play a role in eukaryotic rRNA processing, is encoded by a small family of genes (5-10 copies/haploid genome) in mammals. In mouse, functional genes encoding the major U3B RNA form have been isolated, with all copies identified so far having evolved in a tightly concerted fashion. However, knowledge of the precise number and relative localization of all gene-family members has been hampered by the presence of multiple copies of U3B-processed pseudogenes in the mouse genome. In this study, we took advantage of a probe that is specific for functional U3B genes to address this question, using both Southern hybridization of genomic DNA and in situ hybridization of metaphase chromosomes. We show that the mouse haploid genome contains four functional U3B genes, all of which are clustered in a single chromosomal locus. They map to the C-D bands of mouse chromosome 11, within one of the most extended segments of gene-linkage conservation known between the mouse and human genomes, corresponding to a major portion of human chromosome 17. By contrast, the multiple (nonfunctional) U3 retrogenes are dispersed over several mouse chromosomes.
U3小核仁RNA被认为在真核生物核糖体RNA加工过程中发挥作用，在哺乳动物中由一个小基因家族编码（单倍体基因组中有5 - 10个拷贝）。在小鼠中，已分离出编码主要U3B RNA形式的功能基因，到目前为止鉴定出的所有拷贝都是以紧密协同的方式进化而来的。然而，由于小鼠基因组中存在多个经U3加工的假基因拷贝，阻碍了对所有基因家族成员的确切数量和相对定位的了解。在本研究中，我们利用一种对功能性U3B基因特异的探针，通过基因组DNA的Southern杂交和中期染色体的原位杂交来解决这个问题。我们发现小鼠单倍体基因组包含四个功能性U3B基因，它们全部聚集在一个单一的染色体位点上。它们定位于小鼠11号染色体的C - D带，位于小鼠和人类基因组之间已知的基因连锁保守性最广泛的区段之一内，对应于人类17号染色体的主要部分。相比之下，多个（无功能的）U3反转录基因分散在几条小鼠染色体上。
