Simpson Thacher & Bartlett is representing Chinese internet giant Alibaba Group Holding Ltd. on a $4.2 billion offer to acquire video streaming company Youku Tudou Inc.

In a proposal announced last Friday, Alibaba offered $26.60 per American depository share to buy the 81.7 percent of Youku Tudou it doesn’t already own. The offer represents a 44.5 percent premium to Youku Tudou’s average closing price in the past three months.