Myler P J, Aline R F, Scholler J K, Stuart K D
Seattle Biomedical Research Institute, WA 98109-1651.
Mol Biochem Parasitol. 1988 Jun;29(2-3):243-50. doi: 10.1016/0166-6851(88)90079-5.
In the IsTaR 1 serodeme, we have identified variant surface glycoprotein (VSG) genes in nine different telomeric sites. We have measured the distance from the 3' end of these VSG genes to the end of the chromosome (the 'telomere length') in 20 variant antigen types (VATs) of the serodeme. Analyses of the changes in telomere length during 19 antigenic switches involving eight telomeric sites indicate a median increase in telomere length of 0.6 kilobase pairs during each switch. This may be accounted for by the 6-10 bp increase in telomere length per generation associated with DNA replication described by others. The changes in telomere lengths do not form a normal distribution since a substantial fraction show unusually large increases in telomere length or decreases in telomere length during an antigenic switch. These changes are probably caused by recombinations 3' to the VSG gene. No significant differences were detected in the behavior of telomeres at each of the eight different telomeric sites, nor were changes in telomere lengths significantly different between different antigenic switches. However, it was found that those telomeres where transcription was activated during the antigenic switch showed a significantly greater increase in telomere length than those telomeres not involved in regulation of VSG gene expression. Conversely, there was a strong correlation between transcriptional inactivation of a telomeric expression site and a decrease in telomere length. These findings suggest that processes (possibly genomic recombinations) 3' to the VSG gene coding region may be associated with a change in the transcriptional status of the VSG gene.
在IsTaR 1血清型中，我们在9个不同的端粒位点鉴定出了变异表面糖蛋白（VSG）基因。我们测量了该血清型20种变异抗原类型（VATs）中这些VSG基因3'端到染色体末端的距离（“端粒长度”）。对涉及8个端粒位点的19次抗原转换过程中端粒长度变化的分析表明，每次转换过程中端粒长度的中位数增加为0.6千碱基对。这可能是由其他人描述的与DNA复制相关的每代端粒长度增加6 - 10碱基对所导致的。端粒长度变化并不呈正态分布，因为在抗原转换过程中，相当一部分端粒长度显示出异常大幅的增加或减少。这些变化可能是由VSG基因3'端的重组引起的。在8个不同端粒位点的端粒行为中未检测到显著差异，不同抗原转换之间的端粒长度变化也没有显著差异。然而，发现那些在抗原转换过程中转录被激活的端粒，其端粒长度的增加显著大于那些不参与VSG基因表达调控的端粒。相反，端粒表达位点的转录失活与端粒长度的减少之间存在很强的相关性。这些发现表明，VSG基因编码区3'端的过程（可能是基因组重组）可能与VSG基因转录状态的变化有关。
