SAN FRANCISCO >> A group led by Apple and Microsoft has sold about 4,000 technology patents to patent management company RPX Corp. for $900 million.

The deal announced Tuesday marks another shift in the ownership of a patent portfolio auctioned off in 2011 after telecommunications company Nortel Networks went bankrupt. Apple, Microsoft, BlackBerry, Ericsson and Sony formed the Rockstar Consortium to buy the patents for $4.5 billion, outbidding Google Inc. for the rights to technology used in many mobile devices.

The Nortel portfolio initially consisted of about 6,000 patents, but Apple, Microsoft and the other members of Rockstar held on to 2,000 of them.

RPX, which is based in San Francisco, formed a subsidiary to manage the newly acquired patents and collect licensing payments from more than 30 companies, including Google.