I am not completly sure I understood your question but you could do something like this:
reversedDNA = 'TACATGA'
function complementedDNA = r_dnasepinaka(reversedDNA)
complementedDNA = reversedDNA;
complementedDNA(reversedDNA == 'T') = 'A';
complementedDNA(reversedDNA == 'A') = 'T';
complementedDNA(reversedDNA == 'C') = 'G';
complementedDNA(reversedDNA == 'G') = 'C';
end
and something like this to get all the As:
function [UniqueCharStr , PositionList] = getSingleChar(DNA , Char)
PositionList = find( DNA == Char );
UniqueCharStr = DNA( PositionList );
end
getSingleChar(reversedDNA , 'A')
