CLIP-seq is the state-of-the-art technique to experimentally determine transcriptome-wide binding sites of RNA-binding proteins (RBPs). However, it relies on gene expression which can be highly variable between conditions, and thus cannot provide a complete picture of the RBP binding landscape. This necessitates the use of computational methods to predict missing binding sites. Here we present GraphProt2, a computational RBP binding site prediction method based on graph convolutional neural networks (GCN). In contrast to current CNN methods, GraphProt2 supports variable length input as well as the possibility to accurately predict nucleotide-wise binding profiles. We demonstrate its superior performance compared to GraphProt and a CNN-based method on single as well as combined CLIP-seq datasets.Introduction 1 RNA-binding proteins (RBPs) regulate many vital steps in the RNA life cycle, such as 2 splicing, transport, stability, and translation [1]. Recent studies suggest a total number 3 of more than 2,000 human RBPs, including 100s of unconventional RBPs, i.e., RBPs 4 lacking known RNA-binding domains [2-4]. Numerous RBPs have been implicated in 5 diseases like cancer, neurodegeneration, and genetic disorders [5-7], urging the need to 6 speed up their functional characterization and shed light on their complex cellular 7 interplay. 8 An important step to understand RBP function is to identify the precise RBP 9 binding locations on regulated RNAs. In this regard, CLIP-seq (cross-linking and 10 immunoprecipitation followed by next generation sequencing) [8] together with its 11 popular modifications PAR-CLIP [9], iCLIP [10], and eCLIP [11] has become the 12state-of-the-art technique to experimentally determine transcriptome-wide binding sites 13 of RBPs. A CLIP-seq experiment for a specific RBP results in a library of reads bound 14 and protected by the RBP, making it possible to deduce its binding sites by mapping 15 the reads back to the respective reference genome or transcriptome. In practice, 16 computational analysis of CLIP-seq data has to be adapted for each CLIP-seq 17 protocol [12]. Within the analysis, arguably the most critical part is the process of peak 18 calling, i.e., to infer RBP binding sites from the mapped read profiles. Among the many 19 existing peak callers, some popular tools are Piranha [13], CLIPper [14], 20 PEAKachu [15], and PureCLIP [16].While peak calling is essential to separate authentic binding sites from unspecific 22 interactions and thus reduce the false positive rate, it cannot solve the problem of 23 expression dependency. In order to detect RBP binding sites by CLIP-seq, the target 24 RNA has to be expressed at a certain level in the experiment. Since gene expression 25 naturally varies between conditions, CLIP-seq data cannot be used directly to make 26 condition-independent binding assumptions on a transcriptome-wide scale. Doing so 27 would only increase the false negative rate, i.e., marking all non-peak regions as 28 non-binding, while in fact one cannot tell from the dat...