in the sequence of my gene, there are two ATG. one at the start of sequence and one in the mid region of gene. so now i am confused which one will act as start codon. is it possible that this gene transcribe two transcripts?
Dear Aqib Sayyed, It's common to have multiple ATG codons in an mRNA sequence. Generally, the first ATG serves as protein translation starting site and is considered as a start codon if that ATG is at the beginning of a full and functional open reading frame. This is because the specific motifs and structures of the mRNA sequence has to be integrated correctly into a ribosome, a protein translation machinery, to initiate the translation process. In some cases, two ATG codons are closely located in the 5' end of mRNA, one might generate a truncated protein with few amino acid residues only, but another can result in a functional protein. In this case, the second one can be considered as start codon for that functional protein sequence. This phenomenon is considered as a translational regulation of a functional gene.
Although Shu Wei is entirely correct, I feel you would benefit from reviewing the basics of eukaryotic transcription initiation to further your understanding.
I recommend this article:
http://genesdev.cshlp.org/content/16/20/2583.long
Hello Aqib.
If you cannot find similar characteristics of 5'-UTR sequences before the second ATG, it is a codon for methionine as a component of peptides as in the first ATG (Met).
However, you've got to look at the 5'-UTR of the sequence in any sources online or sequencing the 5'-RACE PCR cloning fragment of the first ATG by yourself.
Best wishes.
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