In bacteria, negatively supercoiled chromosomal DNA is organized by nucleoid-associated proteins. Which set best represents such organizing proteins?

Introduction / Context:
Bacterial chromosomes are compacted without canonical eukaryotic histones. Instead, nucleoid-associated proteins (NAPs) shape and organize negatively supercoiled DNA to enable replication, transcription, and segregation in a crowded cytoplasm.

Given Data / Assumptions:

• We are considering bacterial chromosomal DNA (prokaryotic nucleoid).
• DNA is negatively supercoiled in vivo.
• Proteins that bend, bridge, or wrap DNA contribute to nucleoid architecture.

Concept / Approach:
Among the best-studied NAPs are HU (a small, abundant DNA-bending protein) and H-NS (a global gene-silencing/bridging protein that prefers AT-rich DNA). Together, they compact DNA, stabilize supercoils, and help regulate transcriptional programs in response to environmental cues.

Step-by-Step Solution:

Verification / Alternative check:
Genetic deletions and biochemical reconstitution show HU induces flexible bends, while H-NS oligomerizes to bridge duplexes; both strongly influence nucleoid structure and gene expression.

Why Other Options Are Wrong:

• HU only: incomplete; other major NAPs like H-NS also organize DNA.
• H-NS only: incomplete for the same reason.
• Histone H1: eukaryotic linker histone; not a bacterial NAP.
• HSP-1: chaperone, not a DNA-organizing NAP.

Common Pitfalls:
Equating bacterial DNA proteins with eukaryotic histones, or assuming any DNA-binding protein is a structural organizer.

Final Answer:
Both HU and H-NS