DNA sequence

[ifhmn]

I have searched 4 gene of interest using solanum lycopersicum genomic database. the gDNA sequence of 3 of the genes are in reverse strand (- strand) while 1 of the gene is + strand. So, when I download the whole sequences for example in chromosome 1, I have to reverse complement of my gDNA sequence (- strand) before located them in the chromosome. The question is, why for certain genes, thay use - strand and others use + strand. If I want to look up the promoter sequence (- strand) should I look at the upstream of downstream sequence?

[mchlbrmn]

There is no sense or antisense strand of an entire chromosome, it is arbitrarily assigned (I suppose). Sense is relative to the individual gene's coding sequence, and you look up or downstream relative to that gene for promoter or other elements. So, if two genes overlap then the same sequence can be sense and antisense.

[relaxin]

The question is, why for certain genes, thay use - strand and others use + strand. If I want to look up the promoter sequence (- strand) should I look at the upstream of downstream sequence?

God may be able to answer your first question.

As for the second question, the promoter sequence is likely to be upstream from the Exon 1, but can be embedded within the Exon 1 sequence.