Binds DNA specifically as homodimer or heterodimer with other PAR factors. Isoform HLF43 is abundant in brain, liver and kidney. Isoform HLF36 is expressed only in the liver. Both isoforms accumulate in the liver with different circadian amplitudes. Isoform HLF36 reaches peak expression levels between 8 and 12 p.m. Isoform HLF43 displays a more pronounced fluctuation through the day. Accumulates according to a robust circadian rhythm. Produced by alternative initiation at an unusual initiation codon at position 50. Produced by alternative splicing. Produced by alternative initiation at an unusual initiation codon at position 50. Belongs to the bZIP family. PAR subfamily.