念珠藻Nostoc punctiforme胞外多醣生合成調控機制之預測

Abstract

藍菌念珠藻屬念珠藻屬 (Nostoc) 的胞外多醣胞外多醣 (exopolysaccharides, EPS)生合成相關之遺傳與生化方面的瞭解，目前研究並不多，為探討，為探討念珠藻屬EPS生合成基因可能受到那些轉錄因子調控，進而了解EPS生合成與環境因子的關係，本研究以念珠藻屬中基因體序列已被完整解碼的Nostoc punctiforme ATCC 29133為研究對象，針對其基因體中10個可能參與EPS生合成的基因啟動子區域做序列分析，共預測出15種轉錄因子轉錄因子結合位，藉由與大腸桿菌(Escherichia coli) 轉錄因子結合位序列的相似性相似性比對，預測最有可能會調控EPS生合成基因的轉錄因子為ArgR、Fnr與LexA。最後，利用E. coli K12之ArgR、Fnr與LexA胺基酸序列於N. punctiforme基因體中進行BLAST比對搜尋，結果顯示N. punctiforme具有與具有與E. coliK12相似度極高的轉錄因子LexA，但不具有相似的ArgR與Fnr。因此推測念珠藻N.punctiforme的EPS生合成基因可能會受轉錄因子LexA與其相關環境因子的調控，例如紫外線。

In cyanobacteria Nostoc, the genetics and biochemistry of exopolysaccharide (EPS) biosynthesis have not been thoroughly investigated. To identify the transcription factors that may regulate EPS biosynthesis genes and to understand the relationship between the EPS biosynthesis and the environment factors, in this study, we carried out thein silico promoter analysis of ten EPS biosynthesis-related genes in Nostoc punctiforme ATCC 29133, whose genomic sequence has been determined. Total 15 putative transcription factor biding sites were found in the ten promoter regions. Three transcription factors, ArgR, Fnr, and LexA, were predicted to be the most possible ones by comparing binding site sequence similarity between E. coli K12 and N. punctiforme. Because no ArgR and Fnr homologs were found in N. punctiforme genome by the Basic Local Alignment Search Tool (BLAST) using the amino acid sequences of E. coli K12 ArgR, Fnr and LexA as query sequences, we predicted that N. Punctiforme EPS biosynthetic genes may be regulated by the transcription factor LexA and its associated environmental factors such as UV light.