Studying the expression of a transcription regulatory protein in two cell types, you have performed experiments showing that the mRNA encoding the protein is present at comparable levels in the cytosol of both cell types. However, based on the expression of its target genes, you suspect that the protein activity might be significantly different in the two cell types. Which of the following steps in expression of the gene encoding this protein is more likely to be differentially controlled in these cell types?

a. Translation
b. mRNA transport
c. mRNA degradation
d. Transcription