This paper proposes an extension of the multiversion two phase locking protocol, called EMV2PL, which enables update transactions to use versions while guaranteeing the serializability of all transactions. The use of the protocol is restricted to transactions, called {\em write-then-read} transactions that consist of two consecutive parts: a write part containing both read and write operations in some arbitrary order, and an abusively called read part, containing read operations or write operations on data items already locked in the write part of the transaction. With EMV2PL, read operations in the read part use versions and read locks acquired in the write part can be released just before entering the read part. We prove the correctness of our protocol, and show that its implementation requires very few changes to classical implementations of MV2PL. After presenting various methods used by application developers to implement integrity checking, we show how EMV2PL can be effectively used to optimize the processing of update transactions that perform integrity checks. Finally, performance studies show the benefits of our protocol compared to a (strict) two phase locking protocol.