Hicke B J, Celander D W, MacDonald G H, Price C M, Cech T R
Department of Molecular, Cellular and Developmental Biology, Howard Hughes Medical Institute, University of Colorado, Boulder 80309.
Proc Natl Acad Sci U S A. 1990 Feb;87(4):1481-5. doi: 10.1073/pnas.87.4.1481.
Macronuclear chromosomes of the ciliated protozoan Oxytricha nova terminate with a single-stranded (T4G4)2 overhang. The (T4G4)2 telomeric overhang is tenaciously bound by a protein heterodimer. We have cloned and sequenced the gene encoding the 41-kDa subunit of this telomere binding protein. The predicted amino acid sequence comprises two distinct regions, a carboxyl-terminal two-thirds that is 23% lysine and bears similarity to histone H1 and an amino-terminal one-third containing a hydrophobic stretch of about 15 amino acids. Two macronuclear versions of the gene differ in nucleotide sequence at several positions, but the derived polypeptides differ only at a single position, Ser-110 or Ala-110. Both versions harbor a small intron. The existence of this intron demonstrates that, despite the elimination of 95% of the micronuclear genome from the developing macronucleus, at least some noncoding DNA is retained during macronuclear development of hypotrichous ciliates.
纤毛原生动物新奥克特里查的大核染色体以单链（T4G4）2突出端结束。（T4G4）2端粒突出端被一种蛋白质异二聚体紧密结合。我们已经克隆并测序了编码这种端粒结合蛋白41 kDa亚基的基因。预测的氨基酸序列包括两个不同的区域，羧基末端三分之二富含23%的赖氨酸，与组蛋白H1相似，氨基末端三分之一包含一段约15个氨基酸的疏水序列。该基因的两个大核版本在几个位置的核苷酸序列不同，但推导的多肽仅在一个位置不同，即第110位为丝氨酸或丙氨酸。两个版本都含有一个小内含子。这个内含子的存在表明，尽管在发育中的大核中95%的小核基因组被消除，但在低等纤毛虫的大核发育过程中至少保留了一些非编码DNA。
