When a transcription factor interacts with DNA

histones must be present in the promoter.

covalent bonds are formed so that the factor cannot be removed.

it forms noncovalent bonds with functional groups on the nitrogenous bases.

it interacts only with the sugar-phosphate backbone of the DNA.

it cannot recognize specific bases in the DNA.

The correct answer is histone proteins must be present in the promoter.

Explanation:

Transcription factors act as regulatory proteins or DNA binding proteins which interract with promoter region of a DNA molecule during transciption.

Transcription factor can both upregulate and downregulate the expression of the target DNA to which it interact.

Transcription factors use various processes to regulate gene expression

a Histone Acetylation An enzyme histone Acetyl transferase catalyses the acetylation of epsilon - NH2 group of positively charged lysine residue of histone proteins present in the target DNA. The acetylation result in weakening the interaction between DNA and Histone protein. As a result the target DNA is very much free to undergo transcription thus up regulating the gene expression.

b Histone deacetylation An enzyme histone deacetylase catalyses the removal of additional acetyl group from the acetylated lysine residue of histone protein present in target DNA. As a result the target DNA gets less freedom to carry out transcription thus decreasing or down regulating the gene expression.