Berkshire Hathaway Inc. is in discussions to purchase a 10 per cent stake in Kotak Mahindra Bank. The deal, through which Berkshire may buy promoter stake or get fresh shares, may be valued at $4-6 billion (Rs 28,230-42,345 crore). As per the Reserve Bank of India (RBI) guidelines, Uday Kotak should bring down his stake in the bank to below 20per cent from the current 29.73 per cent by December 2018. Promoter shareholding needs to be further brought down to 15per cent by March 2020. Uday Kotak had earlier sought RBI′s nod for selling nonconvertible perpetual noncumulative preference shares to bring down his stake in the bank to 20 per cent. In August, RBI refused to greenlight the proposal saying it was not acceptable. If the Berkshire deal goes through, it will be Buffett's second big investment in India after the Oklahoma-based company agreed to acquire a stake in Paytm's parent company, One97 Communications Ltd.