calculate expected occurrence of frequency

Question

[ravihansa82]

Dear friends

I need to find out expected occurrence of frequency of given motif for a given DNA sequence. suppose motif is GATAAG, sequence length is 1000 nucleotides. I need to find how many of given motif would be there in such seq as given motif order only.

I tried this way, 1. sequence length is divided by 4^6, but this is having all random mutation of given motif , but I need how much would be there as given order GATAAG without considering mutation in each, can any one suggest a good way