In late afternoon trading, Horizon Discovery shares were up 30.6% at 188p, while Abcam shares gained 2.2% at 1,240p.
In a statement, Abcam said it made a proposal to the board of Horizon Discovery on 19 April 2018 in relation to a possible all share offer which would value each Horizon Discovery ordinary share at 181p each.
It added that the proposal has today been rejected by the Horizon Discovery board.
Abcam said it “believes that the Proposal represents a compelling opportunity to drive superior value creation for the shareholders of both companies.”
“Accordingly,” it added, “Abcam is seeking to engage with Horizon Discovery in a constructive dialogue and is announcing the Proposal as a means to encourage and further that process.”
The group said; “Abcam is executing its vision to be the most influential life science company for researchers worldwide. Horizon Discovery has developed extensive capabilities in the gene editing market and the Board of Abcam believes that the combination of Horizon Discovery's business with Abcam would assist both Abcam and Horizon Discovery to expand their reach and influence globally.”