Wharton KA, Yedvobnick B, Finnerty VG, Artavanis-Tsakonas S (1985). «opa: a novel family of transcribed repeats shared by the Notch locus and other developmentally regulated loci in D. melanogaster». Cell. 40 (1): 55–62. PMID2981631
Rice C, Beekman D, Liu L, Erives A (2015). «The Nature, Extent, and Consequences of Genetic Variation in the opa Repeats of Notch in Drosophila». G3 (Bethesda). 5 (15): 2405–2419. PMID26362765 !CS1 manut: Usa parâmetro autores (link)