Top1

Top1, or TOP1, is a term that may refer to several distinct concepts in science and technology. The most established usage in biology denotes the gene that encodes DNA topoisomerase I, an essential nuclear enzyme found in eukaryotes. The TOP1 enzyme relieves torsional strain in DNA during replication and transcription by producing a transient single-strand break, allowing the DNA helix to unwind, and then resealing the break. This activity helps manage DNA supercoiling and supports transcription elongation. TOP1 is a target for anticancer drugs; camptothecin and its clinical derivatives irinotecan and topotecan bind to the enzyme-DNA cleavage complex, stabilizing it and inducing DNA damage in dividing cells. In humans, TOP1 is expressed in many tissues and operates in the nucleus, with roles in chromatin structure and transcriptional regulation.

In machine learning, top-1 accuracy (often written as top1) is the proportion of instances for which the model’s top predicted class matches the true label. It is a baseline metric for multiclass classification and is frequently reported alongside top-5 accuracy, where the correct label is among the five highest-scoring predictions. The concept is widely used in evaluating image classification, natural language processing, and other datasets.

The term top1 is also used informally to denote the leading position in a ranking or competition, and may appear in esports, sports rankings, or product leaderboards. Context is needed to determine the intended meaning.