SummaryRegardless of their origins, functions, and base compositions, all DNAs are scriptures written following the same grammatical rule. At the level of syllables, two, CG and TA are seldom used, while three, TG, CT and CA are utilized with abundance. Accordingly, at the level of three-letter words, two complementary base trimers, CTG and CAG, invariably enjoy frequent usage. Inasmuch as two of the three frequently used syllables, TG and CA are complementary to each other, while two seldom used syllables, CG and TA, are both palindromes, two complementary strands of DNA are inherently symmetrical with each other. Consequently, palindromic sequences as favourite targets of DNA-binding proteins occur at unsuspectedly high frequencies, if they contain TG and CA or CTG and CAG. Nevertheless, there are grammatical rules operating among these high frequency palindromes as well; e.g. the palindromic tetramer TGCA occurs nearly two times more often than its reciprocal; CATG. Thus, DNA-binding proteins are provided with a wealth of abundant targets whose densities are influenced by a regional difference in GC/AT ratios to variable degrees. One palindromic heptamer CAGNCTG is an ideal target of one DNA-binding protein engaged in chromosome packaging and in generation of banding patterns. This heptamer occurs once every 1000 bases in moderately GC-rich sequences, while its incidence is reduced to once every 3000 bases in extremely AT-rich sequences. The above must be the very reason that a solitary human X-chromosome DNA coated with mouse DNA-binding proteins in mouse-man somatic hybrids still maintains the original banding pattern and that the inactive X remains inactive, while the active X remains active.
TATA Binding Proteins Can Recognize Nontraditional DNA Sequences
