RESUMEN
We expanded the view of Clock (Clk) and cycle (cyc) gene evolution in Diptera by studying the fruit fly Anastrepha fraterculus (Afra), a Brachycera. Despite the high conservation of clock genes amongst insect groups, striking structural and functional differences of some clocks have appeared throughout evolution. Clk and cyc nucleotide sequences and corresponding proteins were characterized, along with their mRNA expression data, to provide an evolutionary overview in the two major groups of Diptera: Lower Diptera and Higher Brachycera. We found that AfraCYC lacks the BMAL (Brain and muscle ARNT-like) C-terminus region (BCTR) domain and is constitutively expressed, suggesting that AfraCLK has the main transactivation function, which is corroborated by the presence of poly-Q repeats and an oscillatory pattern. Our analysis suggests that the loss of BCTR in CYC is not exclusive of drosophilids, as it also occurs in other Acalyptratae flies such as tephritids and drosophilids, however, but it is also present in some Calyptratae, such as Muscidae, Calliphoridae and Sarcophagidae. This indicates that BCTR is missing from CYC of all higher-level Brachycera and that it was lost during the evolution of Lower Brachycera. Thus, we can infer that CLK protein may play the main role in the CLK\CYC transcription complex in these flies, like in its Drosophila orthologues.