WASHINGTON/CHICAGO (Reuters) - Illinois Representative Jesse Jackson Jr., who has been treated for bipolar disorder and has reportedly been under investigation for alleged misuse of campaign funds, resigned his seat on Wednesday.

In a letter to House Speaker John Boehner, the Chicago Democrat said: "My health issues and treatment regimen have become incompatible with service in the House of Representatives. Therefore, it is with great regret that I hereby resign ... effective today, in order to focus on restoring my health."

In his two-page letter to Boehner, an Ohio Republican, Jackson admitted to "my share of mistakes."

"I am aware of the ongoing federal investigation into my activities and I am doing my best to address the situation responsibly, cooperate with the investigators, and accept responsibility for my mistakes, for they are my mistakes and mine alone," Jackson wrote.

(Reporting by Richard Cowan; Writing by Dan Burns; Editing by Jackie Frank)