  Large protein language models are adept at capturing the underlying
evolutionary information in primary structures, offering significant practical
value for protein engineering. Compared to natural language models, protein
amino acid sequences have a smaller data volume and a limited combinatorial
space. Choosing an appropriate vocabulary size to optimize the pre-trained
model is a pivotal issue. Moreover, despite the wealth of benchmarks and
studies in the natural language community, there remains a lack of a
comprehensive benchmark for systematically evaluating protein language model
quality. Given these challenges, PETA trained language models with 14 different
vocabulary sizes under three tokenization methods. It conducted thousands of
tests on 33 diverse downstream datasets to assess the models' transfer learning
capabilities, incorporating two classification heads and three random seeds to
mitigate potential biases. Extensive experiments indicate that vocabulary sizes
between 50 and 200 optimize the model, whereas sizes exceeding 800
detrimentally affect the model's representational performance. Our code, model
weights and datasets are available at
https://github.com/ginnm/ProteinPretraining.
