Question

Once you have sequenced the genome, you still do not know what it means. You just have a sequence of bases. What are ways you can identify if a sequence of DNA is a gene?

Answer 1

Identifying a gene in a sequence of DNA is called gene prediction.

1) One method is where a computer is given instructions for finding gene in a sequence. The computer looks for common sequences like

• Promoter sequences: DNA sequences where transcription of gene by RNA polymerase begins. Usually a sequence of gene includes 5' flaking, exons, introns and flanking region. The sequence in front of first exon is the promoter sequence.
• Start codons: where code for the gene product, RNA, and protein starts. (AUG)
• Stop codons: where code for the gene product ends. ( UAA, UAG, UGA)

2) The other method is using an mRNA sequence and known protein sequences fron the genome. By knowing these sequences we can work backwords by reverse transcription and translation and an idea of the real DNA sequence can be found out.

If we know a protein sequence, the amino acid sequence that make up the protein sequence can also be known, codons that code for the amino acid sequence can also be known and thus the resulting DNA sequence can be found out from it.

For example; Protein sequence: Met-Leu-Ser-Tyr

RNA sequence: AUG-CUU-UCG-UAU

And thus from reverse transcription its DNA sequence can be known.