July 6 (Reuters) - The S&P 500 index opened at a record high on Tuesday, lifted by shares of mega-cap technology firms, while Beijing’s regulatory crackdown hammered shares of several U.S.-listed Chinese firms. The Dow Jones Industrial Average rose 3.8 points, or 0.01%, at the open to 34,790.16. The S&P 500 rose 4.1 points, or 0.09%, at the open to a record high of 4,356.46 , while the Nasdaq Composite rose 22.2 points, or 0.15%, to 14661.548 at the opening bell. (Reporting by Devik Jain in Bengaluru; Editing by Arun Koyyur) Our Standards: The Thomson Reuters Trust Principles.