The invention relates to an isolated nucleic acid sequence comprising a promoter, which is a native sequence of Pichia pastoris comprising the nucleic acid sequence of pCS1 of SEQ ID NO:1, or a functionally active variant thereof which is a size variant, a mutant or hybrid of SEQ ID NO:1, or a combination thereof, expression constructs and recombinant host cells comprising the promoter, and a method of producing a protein of interest under the control of the promoter. It further relates to a method to identify a constitutive promoter from eukaryotic cells, and an isolated nucleic acid sequence comprising a promoter which when operatively linked to a nucleotide sequence encoding a protein of interest directs the expression thereof in a host cell at an expression level that is higher than under control of the native pGAP promoter at high and low growth rates.