UPDATE 1-J&J buys $1 bln stake in Elan, shares soar

* J&J gets 18.4 pct stake in Elan via issue of new shares

* U.S. group takes over interest in Alzheimer's programme

* Relationship with Wyeth to continue

* Elan shares jump 30 percent

(Adds details, background)

LONDON, July 2 (Reuters) - Johnson & Johnson (JNJ.N: Quote, Profile, Research) is take over most of Elan Corp (ELN.I: Quote, Profile, Research) Alzheimer's research and invest $1 billion in new Elan equity in exchange for an 18.4 percent stake in the Irish drugmaker, the companies said on Thursday.

The deal marks the end of a strategic review by Elan (ELN.N: Quote, Profile, Research)(ELN.L: Quote, Profile, Research) and its adviser Citigroup, following pressure from investors for change at the group, which has been burning through cash at a rapid rate.

J&J will initially commit up to $500 million to develop and commercialise Elan's experimental Alzheimer's treatment bapineuzumab and will continue Elan's existing activities with Wyeth WYE.N under their Alzheimer's immunotherapy programme.