OneBeacon Insurance Group, a Bermuda-domiciled holding company, has entered into a definitive agreement to sell its AutoOne business to New York-based Interboro Holdings.OneBeacon, which is part of the White Mountains group, formed AutoOne in 2001 to provide products and services to automobile assigned risk markets primarily in New York and New Jersey.OneBeacon said that the transaction included AutoOne Insurance Company and AutoOne Select Insurance Company, which will contain the assets, liabilities (including loss reserves and unearned premium reserves), and the equity capital of the business.OneBeacon said it expects to record a charge of approximately $28 million pre-tax ($18 million after tax) in its third quarter financial statements reflecting the estimated loss on the sale of AutoOne.OneBeacon CEO Mike Miller said that the transaction allowed the firm to continue focus on the higher performing specialty operations, while aligning AutoOne with an owner committed to serving the personal automobile insurance market.The AutoOne infrastructure including staff, systems and office space is part of the transaction, which is expected to close in the fourth quarter of 2011, subject to the regulator.