With a concrete Sears Roebuck facade and windows filled by trendy Gap jeans, Cambridge's Porter Exchange building seems to have all the elements of mainstream America.

But at this Mass. Ave. mall, American culture hardly penetrates the skin. Sears and The Gap may catch the eye of passing drivers, but inside, names like Kotobukiya and Sapporo draw the crowds.

In the eight years since it opened, the Porter Exchange has become New England's mecca of Japanese culture, drawing customers from New Hampshire, Vermont and Connecticut.

But despite the shopping center's success in attracting Japanese enterprises, the enclave developed mostly by chance.

In 1989 Masa Kuizumi left his job at Boston's up-scale Kyoto Japanese Steakhouse and decided to join several friends who were starting businesses at the Porter Square site.

Although the Asian entrepreneurs didn't start with great expectations, many say they have been enjoying tremendous success in recent years.

"We didn't expect this to happen," said Taisi, a chef who came to Porter Square with Kuizumi.

Taisi explained that his particular store, like many of its neighbors, is beginning to have problems serving all their customers.

"Now it's kind of reaching its maximum. There are only 15 seats here, we can't serve everybody."

Such popularity is due largely to Japanese and Japanese-American customers who find that the Porter Square mall offers the a fleeting taste of home.

Osamu Kaminuma moved from Tokyo to Lowell, Mass., two months ago.

As he was relaxing with his son outside the Kotobukiya grocery store last weekend, Kaminuma explained that the Porter Exchange shops are expensive but remain critical to his family.

"For me it's like I have to come just because it's Japanese," he said.

Kaminuma explained that he usually shops at generic American grocery stores, but makes trips into Cambridge every two weeks for specialty items like spices, sauces and rice.

Kaminuma admitted that another important reason for the trips into Cambridge was to please his young son, who was immersed in a newly purchased Japanese comic book as his father spoke.