When a DNA sequence is presented in scientific journals and databases, it is usually written as a single strand. By convention, the strand shown is the coding (+) or sense strand, identical in sequence (with T's instead of U's) to its mRNA copy. The mRNA then serves as a template for translation, its 5' or upstream sequence (beginning with AUG) corresponding to the NH3-terminal "Met" of the protein.

The complementary DNA strand is called the noncoding or (-) strand and corresponds to the antisense strand. In order to hybridize with and thus detect a specific mRNA, the probe must consist of complementary antisense sequence. Antisense RNA probes are generated when an RNA phage promoter adjacent to more downstream sequence is used.