Abstract
Bacground and Objectives: Start codon is the first codon that can be translated to amino acid after transcription of mRNA from DNA. In all prokaryotes and eukaryotes the genetic code for start codon is ATG that will translate to methionine at the beginning of peptide chain via tRNA, rRNA and other parts of protein synthesis machine but a rare exception was recognized in this universal rule. This kind of exception on universal rule of start codon in eukaryotic genes is important and notable.
Materials and Methods: After isolation, cloning and sequencing of phospholipase B2 gene from pathogenic mold Aspergillus fumigatus (afplb2), usual ATG start codon was not seen at predicted region of obtained sequence and instead of this codon, GTG codon was present at predicted position.
Results: Control of every possible factor for prevention from any mistake for sequences of afplb2 gene were not leads to any mistake and also triple reading of both strand of afplb2 gene were not shown any misreading on the length of cloned gene. Search in the web and submitted genes sequences at different Gene Banks was shown two similar exception on the sequences of start codon and replacement of GTG to ATG on glyceraldehde-3-phosphate dehydrogenase-encoding (gpdA) gene from Phytophotora infestans and gene encoding alpha-aminoadipyl-cysteinyl-valine synthetase (pcbAB) from Cephalosporium acremonium.
Conclusion: It seems that a point mutation has been replaced a purine (G) “guanine” with another purine (A) “adenine” and due to point mutation valine amino acid has been replaced with methionine at the beginning of peptide chain.