Branford-based CuraGen Corp. has completed the sale of its 454 Life Sciences unit to Switzerland-based Roche Holdings Inc. The 167-employee division will remain in Branford as part of Roche Diagnostics. CuraGen formed 454 Life Sciences in 2000 to develop DNA sequencing equipment, which it has sold under a joint marketing and sales agreement with Roche for the last two years. Roche first announced it would buy the unit in March.