Meyer F, Schmidt H J, Heckmann K
Institut für Allgemeine Zoologie und Genetik, Universität Münster, Federal Republic of Germany.
Dev Genet. 1992;13(1):16-25. doi: 10.1002/dvg.1020130104.
We have cloned and sequenced a 1.7 kb macronuclear chromosome encoding the pheromone 4 gene of Euplotes octocarinatus. The sequence of the secreted pheromone is preceded by a 42 amino acid leader peptide, which ends with a lysine residue. The sequence coding for the leader peptide contains information for a putative signal peptide and is interrupted by a 772 bp intron as shown by comparison with a cDNA clone. A 64 bp intron and a 145 bp intron interrupt the sequence coding for the secreted pheromone. The three introns contain typical 5' and 3' splice junctions and a putative branch point site. The small introns have a low GC content. The large intron has a GC content similar to that of the pheromone 4 gene exons. The amino acid sequence of pheromone 4, deduced from both the genomic DNA and the cDNA of pheromone 4, shows that the secreted pheromone consists of 85 amino acids. One of its amino acids is encoded by a UGA codon. Since it has been shown for pheromone 3 of E. octocarinatus that UGA is translated as cysteine, it is assumed that the UGA codon encodes cysteine in pheromone 4 as well. The 164 bp noncoding region upstream of the leader peptide is AT-rich and contains an inverted repeat capable of forming a stem-loop structure with a stem of 11 bp. The 151 bp noncoding region at the 3' end of the chromosome contains a putative polyadenylation sequence and an inverted repeat. The macronuclear molecule is flanked by telomeres and carries the pentanucleotide motif TTGAA, located at a distance of 17 nucleotides from the telomeres. This motif has been suggested to be involved in the formation of macronuclear chromosomes.
我们克隆并测序了一段1.7 kb的大核染色体，它编码八肋游仆虫（Euplotes octocarinatus）的信息素4基因。分泌型信息素的序列之前有一个42个氨基酸的前导肽，该前导肽以赖氨酸残基结尾。编码前导肽的序列包含一个推定信号肽的信息，并且与cDNA克隆比较显示，它被一个772 bp的内含子中断。一个64 bp的内含子和一个145 bp的内含子中断了分泌型信息素的编码序列。这三个内含子包含典型的5'和3'剪接位点以及一个推定的分支点位点。小内含子的GC含量较低。大内含子的GC含量与信息素4基因外显子的GC含量相似。从信息素4的基因组DNA和cDNA推导的信息素4的氨基酸序列表明，分泌型信息素由85个氨基酸组成。其中一个氨基酸由UGA密码子编码。由于已经表明八肋游仆虫的信息素3中UGA被翻译为半胱氨酸，因此推测信息素4中的UGA密码子也编码半胱氨酸。前导肽上游164 bp的非编码区富含AT，并且包含一个能够形成茎环结构的反向重复序列，其茎为11 bp。染色体3'端151 bp的非编码区包含一个推定的聚腺苷酸化序列和一个反向重复序列。大核分子两侧是端粒，并携带五核苷酸基序TTGAA，位于距端粒17个核苷酸的位置。有人认为这个基序参与大核染色体的形成。
