Illinois Rep. Mark Steven Kirk — a Republican centrist who is running for the U.S. Senate in 2010 — received a campaign contribution last month from Republicans for Choice PAC, a group that assists party candidates who support abortion rights.

The $1,000 contribution was reported by the PAC in a filing Wednesday to the Federal Election Commission.

That amount is drop in the bucket next to the millions of dollars that Kirk will raise in his campaign to succeed Roland W. Burris, the appointed Democratic incumbent, who is not running for a full term in the seat that Democrat Barack Obama held when he was elected president in 2008.

Still, the contribution is a reminder of the differences on policy issues between Kirk and the handful of lesser-known but determined conservative opponents he has drawn in the Feb. 2 primary election.

And the donation wasn’t unexpected, as Kirk has repeatedly gone on the record in favor of abortion rights. In June 2003, he was one of five Republicans who voted against banning a particular procedure that opponents call “partial birth” abortion. He also has voted to expand embryonic stem cell research, another position opposed by the conservative “pro-life” movement.