In which domain is the bottom of the DNA-binding cleft? What type of secondary structure lines the bottom of the cleft? In which domain is the bottom of the DNA-binding cleft? What type of secondary structure lines the bottom of the cleft? The bottom of the cleft is in the fingers domain. It is lined with alpha helices. The bottom of the cleft is in the fingers domain. It is lined with a beta sheet. The bottom of the cleft is in the thumb domain. It is lined with both alpha helices and a beta sheet. The bottom of the cleft is in the palm domain. It is lined with alpha helices. The bottom of the cleft is in the palm domain. It is lined with a beta sheet.

During DNA synthesis, a single DNA strand is being built in by polymerization of nucleotides. These polymerization process is catalyzed by enzymes called DNA polymerase. These DNA polymerase can be visualized as an open right hand which is composed of a thumb domain, a finger domain and a palm domain. The palm domain contains a prominent beta-sheet that forms a plate at the button of the DNA-binding cleft.