Lexa may refer to:

• Lexa, Arkansas, a city in Phillips County, United States
• Repressor lexA

Repressor LexA or LexA is a transcriptional repressor  that represses SOS response genes  coding primarily for error-prone DNA polymerases, DNA repair enzymes and cell division inhibitors. LexA forms de facto a two-component regulatory system with RecA, which senses DNA damage at stalled replication forks, forming monofilaments and acquiring an active conformation capable of binding to LexA and causing LexA to cleave itself, in a process called autoproteolysis.