The 5' untranslated region of Arabidopsis thaliana calmodulin cDNA is an independent cDNA containing an open reading frame.

A cDNA clone, pAUK1, with an open reading frame (ORF) coding for a hypothetical 164-amino-acid protein was isolated from an Arabidopsis thaliana (L.) Heynh cDNA library. The clone was attached, tail to tail, to the 3' end of A. thaliana hexokinase cDNA. An almost identical sequence had been previously described as the 5' untranslated region (5' UTR) of A. thaliana calmodulin cDNA (ACaM-2). Sequence comparison with three additional A. thaliana truncated cDNA clones which appear in a database (GenBank) supports the conclusion that pAUK1 is identical to the 5' UTR of ACaM-2 and that the 5' UTR of ACaM-2 is an independent cDNA artificially linked to A. thaliana calmodulin cDNA.