Abstract: The present invention relates to the field of genetic engineering, preferably the expression of recombinant proteins (RP). In particular, the invention relates to a promoter and variants thereof having an equal function and more than 90% sequence identity. The promoter comprises a fragment of 1147 base pairs (bp) of a first promoter, promoter of the ?-actin gene of the Cricetulus griseus genome, enriched in cytosine-guanine dinucleotides (RegCG). The first promoter can be upstream of a second promoter, cytomegalovirus (CMV) promoter. The invention also relates to vectors, transfected cellular lines and a method for producing RP in mammal cells that have been transfected with vectors containing said promoter or variants thereof.