Only last month when it reported its results, RIM said that it was likely to float on the London Stock Exchange next year. The company had wanted to float earlier, but its plans were hit by the economic downturn.
Chris Oakley, chief executive of RIM, said: "In a normal environment, we might have looked to float this year."
The Edinburgh-based Johnston said in a statement that it would raise £220m via a two-for-five rights issue at 280p a share to help fund the deal.
RIM is the former regional newspaper group sold off by United News & Media in 1998 to a group of investors including venture capitalist Candover, which provided 50% of the equity.
RIM publishes titles across Yorkshire and North-West England and South-East Scotland. Its flagship title is the morning daily Yorkshire Post.
Johnston says the acquisition of RIM represents a rare opportunity to strengthen its presence in the tightly held UK regional newspaper market.
Roger Parry, chairman of Johnston Press, says: "This is a transforming acquisition for Johnston Press at a fair price."
At the same time, Johnston also posted full-year results with pre-tax profits for 2001 of £68.5m. The company said it was trading ahead of expectations.
In February, RIM reported an increase in pre-tax operating profit of £44.1m, up by 8% on 2000. Turnover rose 3.5% to £175.3m against £169.3m last time, 84% of which was generated by RIM's newspaper activities. The company said that all advertising categories across the group, except non-local and motors, showed above-inflation growth.
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