Which enzyme is primarily responsible for primer removal and gap filling in bacterial replication?

• A. DNA ligase
• B. Primase
• C. DNA polymerase I
• D. RNA polymerase

Answer: (C)

In bacterial replication, primers are laid down to start synthesis, especially on the lagging strand where short fragments are made. The enzyme that handles primer removal and gap filling is DNA polymerase I. It has a 5' to 3' exonuclease activity that chews away the RNA primer and a 5' to 3' polymerase activity that fills the resulting gap with DNA. After these steps, DNA ligase seals the remaining nick to join the fragments into a continuous strand. The other enzymes play different roles: primase makes the RNA primer, RNA polymerase would be the general transcription enzyme and isn’t the main actor in primer removal during replication, and DNA ligase only seals nicks after the gap has been filled.