三疣梭子蟹基因组微卫星特征分析

Analysis of microsatellite sequences in genome of crab,Portunus trituberculatus

对三疣梭子蟹（Portunustrituberculatus）部分基因组DNA文库测序，获得了总长度为622409个碱基的基因组DNA序列，从中找到微卫星重复序列（1～6bp重复）697个。统计微卫星重复类型，以两碱基重复数目最多，为445个，占微卫星序列总数目的63．84％；其次是三碱基重复152个，占21．81％；再次分别是单碱基重复45个，占6．46％；四碱基重复31个，占4．45％；五碱基重复14个，占2．01％；六碱基重复10个，占1．43％。在单碱基重复类型中，重复拷贝类别全部为A；两碱基重复类型中，AG重复数目最多，其次是AC和AT；三碱基重复类型中以ACT最多，其次是AGG和AA％四碱基重复类型中，AGAC重复数目最多：五碱基重复类型中，以AACCT重复拷贝类别最多；六碱基重复中以AGGGGA重复数目最多。GC重复拷贝类别的重复数目很少，只发现1个（GenBank注册号为EUII3241）。

By sequencing randomly, 4 164 clones of sequences in the genomic library of crab Portunus trituberculatus were obtained. Software DNASTAR （Version 5.0） was used to assemble all of the clones in this study.The length of DNA sequences is about 622 409 bp totally. With the help of the bio-software Tandem Repeats Finder （Version 2.02）, 697 microsatellite repeat sequences are found in the sequences. In the 697 repeat sequences, the number of dinucleotide repeat is 445, being the richest （63.84%） of all the repeat sequences. The second one is trinucleotide repeat with 152 （21.81%） ; the third one is mononucleotide repeat with 45 （6.46%） ; the forth one is tet- ranucleotide repeat with 31 （4.45%） ： the fifth one is petranucleotide repeat with 14 （2.01%） ; the sixth one is hexanucleotide repeat with 10 （1.43%）. Forty-five mononucleotide repeat sequences are all composed of the motif of A, while the motif of C was not found among the mononucleotide repeats. In dinucleotides repeats, the number of AG repeat is 214, accounting for 48.09%; and the numbers of AC and AT repeats are 187 （42.02%） and 43 （9.66%）, respectively. Eight classes of repeat sequences that include motifs of ACT, AGG, AAT, ACC, AAG, ATC, AAC and AGC are found in trinucleotides repeat, in which the number of ACT repeats is the largest with 42; the second one is AGG （35） ; the others are AAT （28）, ACC （21）, AAG （9）, ATC （7）, AAC （7） and AGC （3） in turn. AGAC, AACCT and AGGGGA repeats are the richest ones in tetranucleotide-, pentranucleotide- and hexanucleo- tide-repeat, respectively. Only one GC dinucleotide repeat is found in the study and its GenBank accession number is EU 113241. The reason of fewer GC repeat is possibly that methylation of C in CpG islands results in mutation of C-T or that it is difficult to sequence the GC repeat sequences. Distributions of copy numbers in different types of repeat sequences are as follows： copy numbers of mono- nucleotide repeats are mainly between 28 and 40 or between 68 and 76, accounting for 80.00% totally; copy numbers of dinucleotides are mainly between 12 and 36, accounting for 64.04%; copy numbers of trinucleotides repeats are mainly between 8 and 24, accounting for 57.90%; copy numbers of tetre-, pentra- and hexanucleotides repeats together are mainly between 4 and 12. In general, the length of microsatellite repeat sequences are mainly 24-72 bp. Based on the above, it can be concluded that the nucleotide mutation of microsatellite locations has been accumulated largely in a long term of evolution; and there would be abundant polymorphism in these loca- tions. Therefore, it would be practical to use microsatellite to study the genome of P. trituberculatus and the meth- od would be applied to a variety of fields including population differentiation, kinship analysis, linkage analysis, and evolutional and ecological studies. This study provides base for P trituberculatus microsatellite researches.