No joker — printed, wild or natural — may appear inside a pure sequence. Yet a wild-rank card can sit inside a pure sequence as its real rank: if 7♦ is the wild rank, then 5♦-6♦-7♦-8♦ is a pure sequence because 7♦ is being played as the 7 of diamonds, not as a wild card. This subtle rule decides many declarations — full meld rules: 13-card rummy rules.
Jokers (printed and wild) score 0 points if grouped into a set or sequence. But a joker that never gets melded counts as 10 points — so if your pure sequence is done, spending the remaining jokers on anything legal beats holding them.
Ace is a normal card (10 points; can sit at either end: A-2-3 or Q-K-A with K=10, A=10). A joker may replace an Ace inside any set or impure sequence. Read ace FAQs in the FAQ.