The upgrade to a Buy rating by UBS is a strong positive signal to investors, suggesting improved confidence in Pacific Biosciences' future performance. This typically encourages buying activity, leading to a short-term increase in stock price. However, the reduction in the price target might temper some of the positive sentiment, as it implies a lower expected future price than previously estimated. The net effect is likely to be positive in the short term, as the upgrade to Buy is a more immediate catalyst than the revised price target.