So as can be seen from the discussion above, genes have complex structures, it's not just a case of a particular sequence being a gene or not. Take a typical prokaryotic gene, the sequence can be classified into the following regions:
1) recognition region (
50 bp)
2) transcription initiation site
3) 
untranslated region
4) translation initiation
5) coding region
6) translation stop site
7) 
untranslated region
8) translation stop site
For eukaryotes the structure is similar, except that the ``coding region'' for prokaryotic genes is replaced by an alternating sequence of exons and introns separated by splice sites, and there is a polyadenylation signal to account for.
1) recognition region (
50 kb)
2) transcription initiation site
3) 
UTR untranslated region
4) translation initiation
5) alternating exon/intron, splice donor and acceptor sites
6) translation stop site
7) 
UTR
8) polyadenylation signal
9) transcription stop site