Transcription factors play essential roles in the gene regulation. Structural data on protein-DNA complexes provide clues for understanding the mechanism of protein-DNA recognition. Analysis of these structures has shown that there is no simple one-to-one correspondence between bases and amino acids within protein-DNA complexes, and that the recognition is rather redundant and flexible. We explain the mechanism of such redundant and flexible recognition of DNA sequences by proteins, and describe the methods to predict target DNA sequences in the genome.
The slope of the oxygen equilibrium curve (OEC) of mammalian-hemoglobin (Hb) is maximized at S (oxygen saturation) value of 0.38, and the slope of the S vs. P/P50 (P is partial oxygen pressure; P50 is P at S = 1/2) plot at a P/P50 value of 1 is one-forth that of the Hill-coefficient (n). OECs of mammalian Hbs are designed to have an identical optimal P50 value for O2 delivery and the effectiveness of the Bohr shift (shift of OEC upon pH changes) at O2 loading site. This fact is favorable for uptake and delivery of maximum amount of O2 for fetal blood. To have the identical optimal P50 value for O2 delivery and for the efficiency of the Bohr shift, the relationship, PaO2/PvO2 = ((n + 1)/(n − 1))2/n, is required to hold, where PaO2 and PvO2 are P for arterial and venous bloods, respectively.