  In this work, we study the structure of cyclic DNA codes of arbitrary lengths
over the ring R=F2+uF2+vF2+uvF2 and establish relations to codes over R1=F2+uF2
by defining a Gray map between R and R1^2 where R1 is the ring with 4 elements.
Cyclic codes of arbitrary lengths over R satisfied the reverse constraint and
the reverse-complement constraint are studied in this paper. The GC content
constraint is considered in the last.
