Enables RNA polymerase II transcription regulatory region sequence-specific DNA binding activity and protein heterodimerization activity. Involved in negative regulation of transcription by RNA polymerase II and positive regulation of transcription by RNA polymerase II. Predicted to be located in nucleus. Expressed in digestive tract; egg-laying apparatus; excretory system; neurons; and ventral nerve cord. Human ortholog(s) of this gene implicated in severe acute respiratory syndrome. Is an ortholog of human NFIL3 (nuclear factor, interleukin 3 regulated) and NFILZ (NFIL3 like basic leucine zipper).