Shares of mobile game publisher Zynga (NASDAQ: ZNGA) are soaring on news of a buyout offer from fellow video game company Take-Two Interactive Software (NASDAQ: TTWO). Games formatted for a mobile device have emerged as the biggest revenue generator for the massive and still-growing video game market, which is homing in on $200 billion a year globally. As a result, other publishers have scooped up leading mobile game developers (like Electronic Arts‘ (NASDAQ: EA) takeover of Glu Mobile last summer), and now it’s Take-Two’s turn.