How to use regexp to search for separated sequences?

Say I have a text file with tons of random letters and I want to search it for the sequence ABBA[AGTC]DABA I want ABBA and DABA to be on the ends of the sequence but also want a variable sequence in the middle. GAGA can be either 0, 4, or 6 letters and can be any combination of the letters AGTC.

Any idea how to search for such sequences using regexp? Maybe another search command?

[Star Strider]

Is the ‘variable sequence in the middle’ always enclosed within square brackets []?

Can you provide a sample sequence, or a file with some sample sequences, in the format you expect to use them?

[per isakson]

Are you looking for something like this

>> regexp( 'ABBAAGTGTCDABA', 'ABBA([AGTC]{0}|[AGTC]{4}|[AGTC]{6})DABA', 'match' )
ans = 
    'ABBAAGTGTCDABA'
>> regexp( 'ABBADABA', 'ABBA([AGTC]{0}|[AGTC]{4}|[AGTC]{6})DABA', 'match' )
ans = 
    'ABBADABA'
>> regexp( 'xxxABBAAGTGTCDABAzzz', 'ABBA([AGTC]{0}|[AGTC]{4}|[AGTC]{6})DABA', 'match' )
ans = 
    'ABBAAGTGTCDABA'