Among the various factors binding to DNA elements within the mouse albumin promoter, NF-Y is the only one present at identical concentrations in the nuclei of all examined tissues. NF-Y binds to albumin promoter element C, which contains the sequence CCAAT. To determine whether this factor augments in vitro transcription from the albumin promoter, an extensive point-mutation analysis was performed within the promoter element C. In liver extracts, six out of the ten mutations result in a strong inhibition of NF-Y binding and in a concomitant decrease in promoter activity. Two mutations that increase the affinity of the C-element for NF-Y also augment the transcription efficiency from the albumin promoter. A similarly strong correlation of NF-Y-binding with transcription efficiency has also been observed in spleen nuclear extracts. The liver-enriched CCAAT and enhancer binding factor C/EBP also recognizes the C element. In contrast to NF-Y, no correlation between the affinity of mutant C-elements for C/EBP and transcriptional activity could be observed in liver nuclear extracts.