During initiation of chromosomal replication in E. coli, short RNA primers are synthesized by which enzyme?

Introduction / Context:
DNA replication requires short RNA primers to provide a 3'-hydroxyl for DNA polymerases. Identifying the priming enzyme clarifies the division of labor at the replication fork.

Given Data / Assumptions:

• Organism: E. coli.
• Process: initiation and Okazaki fragment priming.

Concept / Approach:
E. coli uses DnaG primase, a specialized RNA polymerase associated with the DnaB helicase, to synthesize short RNA primers. The housekeeping DNA-dependent RNA polymerase transcribes genes and is not the primase at the fork. Reverse transcriptase is irrelevant in this context.

Step-by-Step Solution:
1) Replication fork assembly recruits DnaG primase to the unwound template.2) Primase synthesizes short RNA oligonucleotides that present a 3'-OH.3) DNA polymerase III extends from these primers; Pol I later removes RNA primers and fills gaps.

Verification / Alternative check:
Genetic and biochemical reconstitution show DnaG activity is essential for Okazaki fragment initiation; depletion prevents lagging-strand synthesis despite the presence of transcriptional RNA polymerase.

Why Other Options Are Wrong:
RNA polymerase (transcriptional): does not normally synthesize replication primers in vivo.Reverse transcriptase: synthesizes DNA from RNA, absent in standard E. coli replication.Both (a) and (b): overbroad; the correct physiological primase is DnaG.

Common Pitfalls:
Equating any RNA-synthesizing enzyme with primase; assuming transcriptional RNA polymerase primes DNA replication.

Final Answer:
Primase